paw coordinate

8/6/2019 Paw Coordinate

1/16

Bra#t Research, 6 6 ( 1 9 7 4 ) 2 3 - 3 8 23E l s ev i er S ci e nt if ic P u b l i s h i n g C o m p a n y , A m s t e r d a m - P r i n t e d in T h e N e t h e r l a n d s

O R G A N I Z A T I O N O F M O T O R A N D S O M A T O S E N S O R Y N E O C O R T E X I NT H E A L B I N O R A T

R O B E R T D . H A L L A ND E R N E S T P . L I N D H O L M *Research Laboratoo' o/ Electronics, Massachusetts In~titute of Technology, Cambridge, Mass. 02139(U.S .A . . )(Accepted July 4th, 1973)

S U M M A R Y

T h e e x t en t a n d o r g a n i z a ti o n o f m o t o r ( M s l ) a n d s o m a t o s e n s o r y ( S m l ) co r te xi n t h e r a t w e r e i n v e s t i g a t e d u s i n g i n t r a c o r t i c a l s t i m u l a t i o n w i th s e m i - m i c r o e l e c t r o d e sa n d s in g le - o r m u l t ip l e - u n it r e c o r d i n g t e ch n i q u es . T w o m a p s o f M s l w e r e p r es e n t e d ,o n e b a s e d o n s t i m u l a t io n w i th 2 5 - m s e c b u r s ts o f a l - k H z s l n u so i d a l c u r r e n t, t h e o t h e rb a s e d o n 2 5 0 - m s e c b u r s t s o f a 3 0 0 - H z s t im u l u s . T h e f i r st o c c u p i e d a r e l a t iv e l y s m a l lr e g i o n o f a n t e r i o r c o r t e x t h a t w a s c o n f in e d t o t h e d o r s a l s u r f a c e o f t h e h e m i s p h e r ea n d d i d n o t r e a c h t h e f r o n t a l p o l e . T h e m o t o r a r e a d e l i n e a t e d w i t h t h e 3 0 0 - H zs t i m u l u s w a s la r g e r , o c c u p y i n g a s i g n if i c an t p o r t i o n o f th e a n t e r o l a t e r a l s u r f a c e a n dm o s t o f t h e f r o n t a l p o l e . M o v e m e n t s o f th e e y e a n d e y e l i d w e r e e l ic i te d f r o m a l o n gt h i n s t r i p o f c o r t e x l y in g n e a r t h e m i d l i n e . T h e v i b r i s s a e w e r e r e p r e s e n t e d i n a n o t h e rl o n g s t r i p a d j a c e n t t o t h e e y e - e y e l i d re g i o n . T h e d e l i n e a t io n o f S m I w a s in g o o da g r e e m e n t w i th e a r l ie r d e s c ri p ti o n s , b u t t h e h i n d l i m b a n d f o r e l i m b a r e a s o v e r l a p p e dt h e ir r e s p e c t iv e m o t o r a r e a s . T h e o v e r l a p w a s e s s e n t ia l ly c o m p l e t e f o r th e h i n d l i m b ,b u t o n l y p a r t ia l f o r t h e f o r e l i m b .

I N T R O D U C T I O N

T h i s s t u d y w a s m o t i v a t e d i n it ia l ly b y a c o n c e r n w i t h c o n t r o l o f th e e y e l idm u s c l e s in t h e r a t . W e w i s h e d t o d e t e r m i n e f i rs t w h e r e t h e e y e l i d s w e r e r e p r e s e n t e d i n' m o t o r ' c o r t e x ( M s I ) . I n d e r i v in g t h e b e st k n o w n , m o s t c o m p l e t e m a p o f t h e r a t 'sm o t o r c o r t e x S e t t l a g e e t a l . 2 3 h a d e m p l o y e d 2 - se c t r a in s o f 6 0 : H z s i n u s o id a i c u r r e n t ,a p p l i e d t o t h e p i a l s u r f a c e t h r o u g h g r o s s e l e c t r o d e s . W e f o u n d i t d i f f i c u l t , h o w e v e r ;t o e v o k e e y e l id r e s p o n s e s r e li a b ly w i t h t h a t k i n d o f s t i m u l a ti o n . M o r e o v e r , t h e e y e l id

* Present address: D epartm ent of Psychology, Arizona State Universi ty, Tempe, Ariz . 85281, U.S.A;


2/16

24 R. D. HAL L AND E. P. LINDHO LMm o v e m e n t s o b s e r v e d b y S e t t l a g e et al . w e r e n e a r l y a l w a y s a c c o m p a n i e d b y o t h e rm o v e m e n t s , o f th e p i n n a o r v i b ri s sa e fo r e x a m p l e ( W o o l s e y , p e r s o n a l c o m m u n i c a -t io n ) . C o n s e q u e n t l y , a m o r e r e li a b le m o d e o f s t i m u l a t i o n w a s s o u g h t t h a t m i g h t a l s oa f f o r d m o r e p r e c i s i o n i n d e l in e a t i n g t h e e y e li d r e p r e s e n t a t i o n in th e r a t ' s m o t o r c o r te x .I n t r a c o r t i c a l m i c r o s t i m u l a t i o n , s u g g e s t e d b y t h e s t u d ie s o f A s a n u m a a n d h is a s s o -c i a t e s 1,,,,'_,4 a n d b y W . W e l k e r ( p e r s o n a l c o m m u n i c a t i o n ) , h a s p r o v e d h e l p f u l i n th i s r e -g a r d . I t h a s , i n a d d i t io n , d i s c lo s e d o t h e r p r o p e r t i e s o f t h e r a t ' s m o t o r c o r t e x , i n c lu d i n ga to p o g r a p h i c a l o r g a n i z a t i o n t h a t d if f er s i n s e v e r al w a y s f r o m t h e o r g a n i z a t i o n d e -s c r i b e d i n e a r l i e r s t u d i e s .

T h e o r g a n i z a t i o n a n d e x te n t o f s o m a t o s e n s o r y c o r t e x ( S m l ) w e r e a l so i n v e s ti g a t-e d , p r i m a r i l y to ai d in d e t e r m i n i n g t h e b o u n d a r i e s o f M s l . T h e e l e c t r o p h y s i o l o g i c a ld a t a i n d i c a t e a n e s s e n t ia l ly c o m p l e t e o v e r l a p o f s e n s o r y a n d m o t o r r e p r e s e n t a t i o n so f th e h i n d l i m b a n d a s ig n i fi c an t b u t p a r t ia l o v e r l a p o f f o r e l i m b a r e a s .METHODS

Sub j e c t sM a l e a l b i n o r a t s o f t h e S p r a g u e D a w l e y s t r a i n , 6 3 i n a l l, w e r e s u b j e c t s . T h e y

w e i g h e d 2 5 0 - 3 5 0 g . F o r t y - e i g h t w e r e u se d i n e x p e r i m e n t s o n t h e m o t o r a r e a , 1 0 ine x p e r i m e n t s d e v o t e d e n t i r e l y t o s o m a t o s e n s o r y c o r t e x , w h i l e 5 w e r e u s e d t o m a pp o r t i o n s o f s e n s o r y a n d m o t o r a r e a s in t h e s ar n e i n d i v id u a l s .P re para t i on

A f t e r a n e s t h e t i z a t io n w i th s o d i u m p e n t o b a r b i t a l ( 6 0 m g / k g ) th e t r a c h e a w a sc a n n u l a t e d , a n d t h e c i s t e r n a m a g n a w a s d r a i n e d t o p r e v e n t s w e l li n g o f th e c o r t e x .T h e l ef t h e m i s p h e r e w a s e x p o s e d , t h e d u r a w a s r e f le c te d , a n d t h e c o r t e x w a s c o v e r e dw i t h m i n e r a l o il w a r m e d t o 3 7 C . W h e n t h e l a te r a l a s p e c t o f t h e c o r t e x w a s i n v e s ti -g a t e d t h e t e m p o r a l m u s c l e , t h e ey e a n d s u r r o u n d i n g t is s u e s w e re ex c is e d . T h e s u b j e c tw a s h e ld r ig i d b y c e m e n t i n g i ts in c i s o r s t o th e m o u t h p i e c e o f a h e a d h o l d e r '3. T h i s e l im -i n a t e d t h e n e e d f o r n o x i o u s c l a m p s o r e a r b a r s a n d l e ft t h e f a c e e a s y t o s e e a n dr e a d i ly a c c e s s i b le f o r ta c t il e s t i m u l a t i o n . T h e a n i m a l s l a y o n a h e a t i n g p a d , a n d r e c ta lt e m p e r a t u r e w a s m a i n t a i n e d a t 35 3 8 C. T h e E K G w a s m o n i t o r e d , a n d t h e p r e p a -r a t i o n w a s c o n s i d e r e d u n s a t i s f a c t o r y u n l e ss w a v e f o r m a n d r a t e w e r e s t a b le . S u p p l e -m e n t a r y d o s e s o f p e n t o b a r b i t a [ w e r e g iv e n a t 0 . 5- h i n t e rv a l s a t a n a p p r o x i m a t e r a l eo f 6 m g / h .Mappin~z o f mo t or c or t e x

S t i m u l a t i n g e l e c t r o d e s w e r e t u n g s t e n o r s t a i n l e s s s t e e l w i r e s , i n s u l a t e d w i t hE p o x y [ i t e , w i t h t ip d i a m e t e r s o f a p p r o x i m a t e l y 1 0 # m . I t w a s n e c e s s a r y t o l e a v e t h et ip u n i n s u l a t e d f o r 0 .5 m m in o r d e r t o e v o k e v i s ib l e m o v e m e n t s . T h e r e f e re n c e el e c-t r o d e w a s u s u a l l y a b r a s s r o d i n t h e r e c t u m , b u t t h e b r a s s m o u t h p i e c e w a s u s e d s o m e -t i m e s w i t h t h e s a m e r e s u l t s .

I n t h e f ir s t s e ri e s o f e x p e r i m e n t s m o n o p o l a r c o r t i c a l s t i m u l a t i o n c o n s i s te d o f2 5 - m s e c b u r s t s o f 1 - k H z s i n u s o i d a l c u r r e n t p r e s e n t e d o n c e e v e r y 2 s ec . S e l e c ti o n o f


3/16

MOTOR ANt ) SOMATOSENSORY CORTEX IN RAT 2~these parameters was based on preliminary observations which indicated that high-frequency, short-duration stimuli evoked small flick movements that were reliableand discrete ( i . e . , involving relatively small parts of the head or body). Stimuli of' longduration were unsatisfactory because prolonged use led to dissolution of the electrodeand discoloration of the tissue surrounding it.The motor area delineated by the l-kHz stimulus occupied a much smaller areathan the responsive area found by Settlage et a l . 23 . Consequently, additional experi-ments were conducted using a 300-Hz sinusoid with a duration of 250 msec and repe-tition rate of 1/2 rain. These stimuli were more like those used by Setttage e t a l . , butthey still evoked small discrete movements. There was no apparent electrode damageunless the tip was smaller than 10#m. Throughout these experiments stimuluscurrents were continually monitored on an oscilloscope by displaying the voltagedr op ac ross a 100 ~ resistor in series with the electrode. All stimulus levels reportedhere were determined this wa~.A current of 200/zA was used to search for responsive areas. The electrode waslowered slowly through the cortex as the 1-kHz stimulus was presented, but becauseof the low repetition rate used with the 300-Hz stimulus the electrode was advancedin discrete steps of 0.25-0.50 mm. In many penetrations estimates of thresholdswere made at each depth beginning at the point where movement s first appeared inresponse to the search stimulus. In every penetration an esumate of the thresholdwas obtained in order to determine if it were low enough that the data point couldbe accepted as valid. This was done by measuring the amount of current that evokeda response approximately 50'~'~',of the time at a depth where the response was evokedwith the weakest stimulus during a penetration. This was relatively easy with the1-kHz stimulus since it was possible to make many measurements in a short time.It was much more difficult to get good estimates of thresholds at different depthswith the 300-Hz stimulus. By that stage of the experiments, however, it was clearthat the lowest thresholds were deep in the cortex and, consequently, it was no1necessary to estimate thresholds through the whole depth of the cortex in mostcases. Electrode penetrations were made perpendicular to the cortical surface, usuallyat 0.5 mm intervals along an imaginary rectilinear grid whose origin was bregma.Larger or smaller steps were often necessary to avoid blood vessels on the surface.Cortex comprising the medial wall of the hemisphere was nol studied because oldiffculties in achieving perpendicular penetrations. The number of penetrations inindividual animals varied fr om only a few to more than 100. The entire mo to r areawas not explored in a single rat, but overlapping cortical areas were studied in suc-cessive experiments and the data were combined using the coordinates employed inthe experiments. No attempt was made to obtain histological information about theelectrode sites where movements were elicited.M a p p i n g o f s om a t o s e n so r y c o r te xSingle- or multiple-unit responses to light tactile stimuli were recorded withmicropipette electrodes with tip diameters of 1-6 #m. Electrodes were filled with


4/16

26 R. D, HALL AND E. P. [INDHOLM3 M KC1. A Grass P-16 preamplifier with high impedance probe was used to amplil~.the potentials that were then monitored on an oscilloscope and loudspeaker.The electrode was advanced slowly through the cortex as the body was strokedor tapped with a wooden probe or palpated with the fingers. When a response wasobtained effor ts were made to isolate a single unit. The location o1" its receptive lieldwas determined by noting where brisk movement of hairs or light laps of glabrousskin with a small wooden probe evoked discharges. Multiple-unit responses in whichsome discharges clearly originated near the electrode tip were also accepted it" theywere evoked in restricted areas of the body surface. In all, 320 penetrations yieldedpositive responses whose peripheral origins were determined with confidence.In 4 experiments rats were immobilized with D-tubocurarine chloride (4 mg/kg)and pentobarbital anesthesia was discontinued. These rats were artificially respiredat a rate of approximately 60/rain and a volume of approximately 2.5 ml. Woundmargins were infiltrated periodically with 2'!ii xylocaine chloride. The,'e were no pres-sure points to cause discomfort. Supplementary doses of D-tubocurarine ~l mg/kg)were given at the first sign of movement. In 6 other experiments pentobarbital anesthe-sia was maintained throughout by supplementary doses ot"3 mg every 0.5 h, althoughthe animals were also immobilized with D-tubocurarine. Data fl'om both sets of ex-perilnents have been combined as there were no obvious differences between them.Sensory and motor mapping in the ,same sul?/ectIn 5 experiments both sensory and motor properties of restricted areas wereexamined in each animal in an effort to shed light on the question of overlap in sen-sory and m oto r representations. Hindlimb or forelimb sensory areas were tirst mappedin rats under light pentobarbital anesthesia as described above. Care was taken toassure that responses were evoked by light tactile stimuli and not by greater pressuresthat might disturb deep tissues or produce movement. Effects of the D-tubocurarinewere allowed to dissipate in 4 experiments in which it was used during the sensorymapping. It was then determined where in the same area movements could be evokedby the 300-Hz sinusoidal current. The same low threshold criteria were employed asin mapping Msl.RESULTS

Cortical motor areasStimulus currents required to evoke movements ranged from 15ttA to morethan 500/, A. Movements with thresholds greater than 200 irA, for the 1-kHz stimulus,or 150/tA, for the 300-Hz stimulus, have been disregarded in the following summary.Higher currents usually evoked movements that involved more than one part of thebody, and the patterns of such movements were frequently unstable, differing fromone stilnulation to the next. The boundaries of responsive cortex indicated beloware arbitrary, then, in the sense that movements can be evoked by stronger stimulibeyond those boundaries. Nevertheless, use of only the low threshold data has madeit possible to compare and to combine dat a on similar kinds of movemen ts in different


5/16

M O T O R A N D S O M A T O S E N S O R Y C O R T E X I N R A 'I- 2 /

F i g . 1 . M o t o r a r e a d e l i n e a t e d b y d e p t h s t i m u l a t i o n wi t h 2 5 - m s e c b u r s t s o f a 1 - k Hz s i n u s o i d a l c u r x e n t.A r e a is b a s e d o n p o o l e d d a t a f r o m 3 3 r at s s u m m a r i z e d i n F i g . 2 . O r i g i n o f g r id i n t h is a n d s u c c e e d i n gf i g u r e s i s b r e g m a ; u n i t s a r e m m . E , e y e ; E L , e y e l i d s ; V , v i b r i s s a e ; F L , f o r e l i m b ; H L , h i n d t i m b ;T , t r u n k ; R , r h i n a r i u m ; J , j a w ; L , li p ; T o , t o n g u e . T h e r e p r e s e n t a ti o n o f t h e b r a i n a n d t h e c o o r d i n a t es y s te m a r e a m o d i f i c a ti o n o f o n e b y L i b o u b a n - L e t o u z e ~'~.

a n i m a l s , a n d t o d o s o w i t h o u t f e a r o f c o n t a m i n a t i o n b y r e fl ex r e s p o n s e s t o s t i m u l a t io no f th e d u r a o r o t h e r t is s ue s . A c o n s i s t e n t p i c tu r e o f t h e t o p o g r a p h i c a l o r g a n i z a t i o n o ft h e m o t o r a r e a h a s e m e r g e d u n d e r t h e s e c r i t e r i a .

T h e m o t o r a r e a d e l in e a t e d b y th e l - k H z s t im u l u s i s s h o w n i n F ig . 1. I t o c c u p ie so n l y th e d o r s a l p o r t i o n o f a n t e r i o r c o r t e x a n d d o e s n o t e x t en d t o t h e f r o n ta l p o l e .T h e a r e a r e s p o n s i v e t o s h o r t b u r s t s o f h i g h - f r e q u e n c y s t i m u l a t i o n i s, t h e r e f o r e , s m a l l e rt h a n t h e m o t o r a r e a d e l im i t e d b y S e t tl a g e e t a l . ~ 3 . W i t h o n e n o t a b l e e x c e p t io n , h o w -e v e r , t h e i n t e r n a l o r g a n i z a t i o n o f th e m a p in F i g . 1 a n d i t s g e n e r a l o r i e n t a t i o n a r eq u i t e s i m i l a r t o t h a t o f th e c l a s si c al m a p . T h e e x c e p t i o n i s th e l o n g s t r i p o f c o r t e x n e a rt h e m i d l i n e w h e r e m o v e m e n t s o f th e e y e a n d e y e l id w e r e ev o k e d .

T h e i n t e r n a l o r g a n i z a t i o n o f th e f o r e li m b , t r u n k a n d h i n d l i m b a r e a s h a s n o tb e e n s p e c i fi e d . O n e r e a s o n f o r th i s is t h a t t h e v a r i e t y o f m o v e m e n t s d i s p l a y e d b y al i m b o r t r u n k i n a s i n g l e e x p e r i m e n t w a s u s u a l l y l i m i t e d w i t h t h e s a m p l i n g p r o c e d u r e st h a t w e r e u s e d. I t w a s o f t e n t h e c a s e . t o o , t h a t a p a r t i c u l a r m o v e m e n t s e e m e d p r e -p o t e n t ; s t i m u l a t io n a l m o s t a n y w h e r e w i t h in t h e f o r e l im b r e g i o n m i g h t e v o k e t h es a m e m o v e m e n t . E x t e n s io n o f t h e w r is t w a s o f t e n o b s e r v e d a s s u c h a r e s p o n s e , th o u g ha d d u c t i o n o f t h e f o r e l e g o r e x t e n s i o n o f a s in g l e d i g i t w e r e f r e q u e n t r e s p o n s e s a l s o .A b d u c t i o n o f th e l i m b o r e x t e n s i o n o f a d ig i t w e r e th e m o s t f r e q u e n t r e s p o n s e s o f t h eh i n d l im b . T h e v i b ri s sa e a re a d i d e x h i b it m o r e i n t er n a l o r g a n i z a t i o n . M o v e m e n t s o f th ea n t e r i o r a n d d o r s a l m y s t a c i a l v i b r is s a e w e re m o s t r e l ia b l y e v o k e d b y s t i m u l a t i o ni n t h e a n t e r i o r a n d m e d i a l v i b r is s a e a r e a : t h e v e n t r a l a n d p o s t e r i o r v i b r i s s a e w e r er e p r e s e n t e d i n th e p o s t e r i o r a n d l a te r a l p o r t i o n o f th e a r e a . M o v e m e n t s o f th e v ib r i s s aew i t h n e a r t h r e s h o l d s t i m u l i w e r e f li ck s o f a s i n g le h a ir . o r a t m o s t a f e w a d j a c e n th a ir s . T h e m o r e p r e c i s e o r g a n i z a t i o n o f t h e v i b ri s s a e a r e a h a s n o t b e e n i n d i c a te d i nF i g . 1 , a n d t h e le v e l o f p r e c i s i o n i n d i c a t e d t h e r e f o r t h e v a r i o u s b o d y s e g m e n t s h a sb e e n a d o p t e d f o r t h i s r e p o r t .


6/16

28 R. D. H ALL AND E. P. t . INDHOLM

F ig . 2 . G r ou p da ta on w h ic h F ig. 1 i s ba se d . M ove m e n t o f a pa r t i c u la r pa r t o f t he bod y i s i nd ic a t e da t a g ive n loc a t ion i f i t w a s e voke d in one o r m ore r a t s a t t hose c oo rd ina te s . O ve r l a pp in g sym bo l sind ic a t e t ha t d i f f e re n t mo ve m e n t s w e re e li c i te d a t t ha t l oc a t ion in d i f f e ren t r a ts . , ,, v ib r i s sa e ; O ,f o r e l i m b ; , ~ :, t r u n k , A , j a w , li p a n d t o n g u e ; V , e y e l id ; , , h i n d l i m b . D a t a p o i n t s f o r r h i n a r i u ma nd e ye a re no t p lo t t e d in o rde r t o a vo id e xc e ss ive c row d ing .

A s u m m a r y o f 2 8 0 p o s it iv e d a t a p o i n t s f r o m 3 3 a n i m a l s o n w h i c h F ig . 1 i sb a s e d i s p r e s e n t e d i n F i g . 2. T h e i n i t ia l i m p r e s s i o n f r o m F i g . 2 is o n e o f c o n s i d e r a b l eo v e r l a p ; m o r e t h a n o n e k i n d o f m o v e m e n t w a s f o u n d a t m o s t l o ca t io n s . B u t th ei m p r e s s i o n is m i s l e a d i n g , a n d t h e a p p a r e n t o v e r l a p r e s u lt s f r o m c o m b i n i n g d a t af r o m d i f f e r e n t r a t s w i t h n o t h i n g m o r e t h a n a f e a t u r e o f t h e s k u ll a s a r e f e r en c e .I f w e c o n s i d e r t h e d i f f ic u l t y i n i d e n t i f y i n g b r e g m a a s a ' p o i n t ' a n d t h e i n h e r e n tv a r i a b i l i t y o f b o n e s a n d t h e i r s u t u r e s , n o t t o m e n t i o n v a r i a b i l i t y in th e b r a i n , i t i ss u r p r i s i n g t h a t t h e o v e r l a p b e t w e e n a n y t w o b o d y s e g m e n t s r a r e ly e x c e ed s 0 .5 r a m .T h i s i s a s l it t l e a s o n e m i g h t e x p e c t w i t h t h e s p a t i a l r e s o l u t i o n o f th e s a m p l i n g , a n d i ts u g g e st s t h a t i f t h e r e i s a n y o v e r l a p o f th e r e p r e s e n t a t i o n s o f d i f f e r en t b o d y s e g m e n t sit m u s t b e l e ss t h a n 0 . 5 r am . T h i s i s b o r n e o u t b y d a t a f r o m i n d i v i d u a l r a t s l i ke t h o s ei l l u s t r a t e d i n F ig . 3. I n a n y c a s e , th e m o v e m e n t s e v o k e d a t a p a r t i c u l a r s i t e w e r e a l w a y sr e s t r i c te d t o a d i s t i n c t i v e p a r t o f t h e fa c e o r b o d y a t n e a r t h r e s h o l d s t i m u l u s i n t e n s i t i e s .

F ig . 3. Co r t i c a l l oc a t ions in one r a t w he re mo ve m e n t s w e re e voke d by de p th s t imu la t ion w i th 25- re se to f 1 -kH z s inuso ida l c u r re n t . X s ( ,~ ) i nd ic a t e s i te s , , ,, .h e re low th re sho ld mo ve m e n t s c ou ld no tb e e v o k e d . ( ) , v i b r is s a e ; O , f o r e l i m b ; . , , t r u n k : i , j a w ; V , e y e l i d ; ~ , r h i n a r i u m : ! I, t o n g u e ;. , h i n d l i m b ; ~ , v e n t r a l n e c k o r c he st .


7/16

MOTOR AND SOMATOSENSORYCORTEX IN RAT 2g

Fig. 4. Group data showing cortical locations where movements were evoked by depth stimulationwith 250-msec bursts of 300-Hz stimulus. Overlapping symbols indicate that different movementswere elicited at that location in different rats. ~q, vibrissae; O, forelimb, ~ , hindlimb; A, trunk;A, jaw, lip, tongue; V, eyelid; O, rhinarium.

The small cortical area that responded to the l-kHz stimulus is quite apparentin Fig. 3 where negative points bord erin g the responsive area are also indicated. I t wasthe smallness of this area that prompted the remapping with the 300-Hz stimulus oflonger duration.A summary of 305 points where the 300-Hz stimulus was effective is shown inFig. 4. The responsive area is clearly larger than the area responsive to the l-kHzstimulus and includes the anterolateral surface and most of the frontal pole. Somegaps in the plotted points indicate that it was not always possible to evoke low-threshold movements within the area circumscribed by those points. Some gapssimply indicate that points were not sampled because considerable time was spentin some experiments investigating restricted areas and special problems, most notablythose concerning the representation of eye and eyelid movements. Data summarizedin Fig. 5 indicate that the areas fr om which eye and eyelid movemen ts could be evokedwere essentially coextensive. This same picture emerged from experiments in whichthe 1-kHz stimulus was used.

Fig. 5. Group data showing cortical locations where eyelid (O), eye (A), or both eye and eyelid (1 )movements were evoked by 300-Hz stimulus.


8/16

30 R . D . H A L L A N D E . P . L I N D H O L MMovements of the eye or eyelids were sometimes obtained from the same loca-tion in the same animal at different times. In some cases it was impossible to separatethe two kinds of movements. In others, which type of movement occurred seemed todepend on the state of the preparation, and in particular on the condition of orbitaltissues. Eyelid responses were observed most readily if the eyelids were partly closedto begin with. One reason for this was that movements of the lids evoked by corticalstimulat ion always increased the size of the palpebral fissure. Blinks were never ob-served, not even partial closures. The movements were also small and often difficultto see without the aid of a dissecting microscope. In some preparations an exoph-thalmia developed, and in some of these the conjunctiva appeared swollen. Move-ments of the lids were not seen under these conditions, but movements of the globewere. Such eye movements were evoked sometimes from the same location whereeyelid movements had been evoked earlier. It was our impression that, in someexperiments at least, the exophthalmia was directly related to the amount of stimu-lation or the number of penetrations in the eye-eyelid region of motor cortex. In anycase, it could not be attributed to a general deterioration of the preparation because,(a) protrusion of the globe appeared only on the side contralateral to the exposedhemisphere, (b) thresholds for other movements were comparable to those foundearlier in the experiment, (c) the exophthalmia was rare in experiments in which theeye-eyelid area was not investigated.The small eyelid movements, their unexpected direction, and their close asso-ciation with movements of the eye suggested that they might be passive, secondary tomovements of the globe, rather than the result of eyelid muscle activity. This possi-bility was investigated in two rats in which all of the eye muscles were cut at their

insertions. Eyelid movements were observed under these conditions that were likethose tbund with intact eye nmscles.An outline of the areas from which movements were evoked by the 300-Hzstimulus is presented in Fig. 6. Although the motor area defined by this stimulus islarger than the area delimited by the l-kHz stimulus, its internal organization is thesame. The enlargement was accomplished by the expansion of facial areas into an-terior and anterolateral regions without significant encroachment of one area uponthe other. The foreleg area also expanded slightly in the anterolateral direction, butposterior and medial borders of the motor area changed only slightly with the changein stimulus parameters. The vibrissae representation includes the area where move-ments of the rhinarium were evoked; vibrissae movements within that area werealso common. The extensive representation of vibrissae is noteworthy.Jaw, lip and tongue movements were interspersed in the same general region,and no attempt was made to order them further. Jaw movements were always asimple lowering of the jaw: coor dinat ed movements of mastication were not observed.On the other hand, a variety of tongue movements was seen; rapid extension andbrief elevations of the tip or medial parts of the tongue were the most frequent.All move ments evoked by the 300-Hz or l-kHz stimuli were on the contralateralside of the body. Bilateral responses, particularly of the face, were seen frequently:but in nearly every case the ipsilateral component was eliminated by reducing the


9/16

M OTOR AN D SOM ATOSENSORY CORTEX I N RAT ~qi

F i g . 6 . M o t o r a r e a s ( s o l i d l i n e s ) b a s e d o n g r o u p d a t a o f F i g . 4 f o r 3 0 0 - H z s t i m u l u s , a n d p r i m a r ys o m a t o s e n s o r y a r e a s ( b r o k e n l i n e s ) b a s e d o n s i n g l e - o r m u l t i p l e - u n i t r e s p o n s e s t o l i g h t t a c t i l e s t i m u l ir e c o r d e d f r o m 1 6 r a ts . E , e y e ; E L , e y e l i d : V , v i b r i s s a e ; F L , f o r e le g ; H L , h i n d l e g ; T , t r u n k ; R ;r h i n a r i u m ; H , b e a d ; J , j a w ; L , l ip ; T o , t o n g u e .

s t im u l u s i n t e n s it y . M o v e m e n t s e v o k e d b y t h e t w o k i n d s o f s t i m u l a t i o n d i d d i f f er ins o m e r e sp e c ts . T h e y t e n d e d t o b e m o r e e x t e n s iv e w h e n e v o k e d b y t h e s t im u l u s o fl o w e r f r e q u e n c y a n d l o n g e r d u r a t i o n . F o r e x a m p l e , f o r e l im b m o v e m e n t s e v o k e d b yt h e 3 0 0 - H z s t im u l u s w e r e u s u a l ly a n a d d u c t i o n o f th e l i m b . o r a n e x t e n s io n o r r o t a -t io n o f t h e w r is t. W i t h t h e l - k H z s t im u l u s a l a r g e r p r o p o r t i o n o f b o t h f o r e l i m b a n dh i n d l i m b r e s p o n s e s w e r e m o v e m e n t s o f th e d i g it s. T h e i n it ia l p o s i t io n o f th e l i m ba l s o p l a y e d a r o t e in d e t e r m i n i n g t h e m o v e m e n t . I f, f o r e x a m p l e , t h e l i m b w e r e p l a c e di n a n e x t e n d e d p o s i t io n a w a y f r o m t h e b o d y j u s t b e f o r e t h e c o r t e x w a s s ti m u l a te d .a d d u c t i o n w a s m o r e l ik e ly to o c c u r t h a n o t h e r m o v e m e n t s w i th n e a r t h r e s h o l d s t im u l i.

S o m e k i n d s o f m o v e m e n t s w e re e n c o u n t e r e d m o r e f r e q u e n t l y t h a n o t he r s.M o v e m e n t s o f t he v i b r i ss a e a n d f o r e l i m b w e r e e a si ly e v o k e d i n e v e r y p r e p a r a t i o na n d , c o n s e q u e n t l y , w e r e u s e d a s fr e q u e n t c h e c k s o n t h e c o n d i t io n o f th e p r e p a r a t i o n .O n t h e o t h e r h a n d , m o v e m e n t s o f th e p i n n a w e r e se e n o n o n l y a f e w o c c a s i o n s , a n dm o v e m e n t s o f th e t ai l w er e n e v e r e n c o u n t e r e d . M o v e m e n t s o f t h e n e c k m u s c l es .s u r p r is i n g ly , w e r e a m o n g t h o s e s e e n in f r e q u e n tl y . T h e r e w e r e n o a p p a r e n t d i f fe r e n ce si n th r e s h o l d s b e t w e e n m o v e m e n t s s e e n i n f r e q u e n tl y a n d t h o s e o b s e r v e d in m o s te x p e r i m e n t s , i f o n e c o n s i d e r s o n l y m o v e m e n t s w i th t h r e s h o l d s b e l o w t h e t h r e sh o l dc r i te r i a t o b e g i n w i t h . F o r t h e c a t e g o r ie s o f m o v e m e n t s u s e d i n F ig s . 1 - 6 , m e a n p e a k -t o - p e a k t h r e s h o l d c u r r e n t s w e r e 7 9- 1 31 ,u A fo r th e 1 - k H z s ti m u l u s a n d 7 0 - t 2 0 / z Af o r t h e 3 0 0 - H z s ti m u l u s. T h r e s h o l d s f o r al l k in d s o f m o v e m e n t s w e r e lo w e r w i t h t h e3 0 0 - H z s t i m u l u s t h a n w i t h t h e 1 - k H z s ti m u l u s , t h e m e a n d i ff e r e n c e b e i n g 2 4 , u A .T h e s e t h r e s h o l d m e a s u r e m e n t s a r e o n l y a p p r o x i m a t i o n s , a s th e r e w a s n o a t t e m p t t om a k e p r e c i s e d e t e r m i n a t i o n s u n d e r i d e n t ic a l p r o c e d u r e s i n ev e r y p e n e t r a t i o n . T h e r eis , h o w e v e r , n o r e a s o n t o b e l ie v e t h a t t h e m e a s u r e m e n t s a r e b i a s e d , e x c e p t t h a t o nt h e w h o l e t h e y a r e p r o b a b l y h ig h . A b s o l u t e t h r e s h o l d m e a s u r e m e n t s r e q u ir e o p t i m i -z a t io n o f m a n y v a r i a b l e s, e.g., l e v el o f a n e s t h e s i a , e l e c t r o d e d e p t h , p o s i t i o n o f t h eb o d y , e tc . , so t h a t i t i s d i ff ic u l t t o m a k e p r e c i s e d e t e r m i n a t i o n s a n d c a r r y o u t t h em a p p i n g i n t h e s a m e e x p e r i m e n t . C a r e w a s t a k e n t o o p t i m i z e c o n d i t i o n s i n 3 e x p e r i-


10/16

32 R . D . H A L L A N D g . P . L IN D H O L Mm e n t s w h o s e m a i n p u r p o s e w a s t o m e a s u r e t h r e s h o l d a s a f u n c ti o n o f d e p t h i n t h ec o r t e x . T h r e s h o l d s w e r e 9 - 1 0 t i m e s g r e a t e r n e a r t h e s u r f a c e , w h e r e t h e y w e re 3 00 4 2 0M A , t h a n a t d e p t h s o f 1 .5 2 .0 m m w h e r e t h e y w e r e 3 0 - 4 5 I ~A . E s t i m a t e s o f th e d e p t h sw e r e o b t a i n e d f r o m m i c r o m e t e r r e a d i n g s a n d m a y b e a b i t l a rg e b e c a u s c o f a s l ig h td e p r e s s i o n o f th e c o r t e x b e f o r e t h e e le c t r o d e p e n e t r a t e d t h e p i a : b u t t h e s y s t e m a t i cd e c r e a s e s i n t h r e s h o l d s w i t h in c r e a s i n g d e p t h w e r e u n m i s t a k a b l e . T h r e s h o l d m e a s u r e -m e n t s m a d e i n e a c h p e n e t r a t i o n , i t m i g h t b e n o t e d , w e r e f o r t h e s a m e m o v e m e n t , o r a tl ea s t f o r m o v e m e n t s o f t h e s a m e p a r t o f th e b o d y . D u r i n g t h e m a p p i n g e x p e r i m e n t sm o v e m e n t s o f d i f fe r e n t p a r t s o f th e b o d y w e r e o c c a s i o n a l l y s e e n a t d i ff e r en t d e p t h so f a p a r t i c u l a r p e n e t r a t i o n , b u t t h e m o v e m e n t s w it h th e l o w e s t t h r e s h o l d s w e r ef o u n d a t d e p t h s o f 1 .5 2 . 0 m m , a n d i t is t h e s e r e s p o n s e s t h a t w e r e i n c l u d e d i n t h e d a t ar e p o r t e d h e r e .P r im a r .l ' s o m a l o s e n s o r y c o r t e x

S i n g l e - o r n m l t i p l e - u n i t r e s p o n s e s t o l i g h t t a c t i l e s t i m u l i w e r e f o u n d i n t h e a r e a so u t l i n e d b y d a s h e d l i n es in F ig . 6. O r g a n i z a t i o n w i t h i n a r e a s d e v o t e d t o m a j o rs e g m e n t s o f t h e b o d y h a s n o t b e e n i n d i c a t e d i n o r d e r t h a t o v e r a l l r e l a t io n s h i p sb e t w e e n s e n s o r y a n d m o t o r a r e a s w o u l d b e c le a r. O v e r l a p in h i n d l i m b a n d f o r e l i m br e g i o n s i s i m m e d i a t e l y a p p a r e n t . I t a p p e a r s t o b e e s s e n t ia l ly c o m p l e t e i n th e h i n d li n abr e p r e s e n t a t i o n s , b u t o n l y p a r t i a l f o r t h e f o r e l i m b . S e n s o r y a n d m o t o r r e p r e s e n t a t i o n so f th e h e a d e x h i b i t e d n o o v e r l a p , b u t i t s h o u l d b e p o i n t e d o u t t h a t t h e a n t e r o l a t e r a lb o u n d a r i e s o f t h e s e n s o r y h e a d a r e a a n d t h e p o s t e r o l a te r a l b o u n d a r y o f t h e m o t o rr e p r e s e n t a t i o n o f j a w , l ip , a n d t o n g u e w e r e d e t e r m i n e d f r o m r e l at i v e ly fe w d a t a p o i n t s .I n t e r e s t c e n t e r e d o n t h e d o r s a l c o r t e x w h e r e t h e q u e s t i o n o f o v e r l a p b e c a m e o b v i o u sf o l lo w i n g t h e i n it ia l m a p p i n g o f S m l .

F ig . 7 a s u m m a r i z e s 2 28 e l e c t ro d e p e n e t r a t i o n s y i e l d in g p o s i t iv e r e s p o n s e s o nw h i c h s e n s o r y f o r e l i m b , h i n d l i m b a n d t r u n k a r e a s in F i g. 6 a r e b a s e d . O v e r l a p o f

o co

6 5

b

5 24 \ .5 a ~ . o J

F i g . 7. a : G r o u p d a t a s h o w i n g l o c a t i o n s o f si n g l e - o r m u l t i p l e - u n i t r e s p o n s e s t o t a c t il e s t i m u l a t i o no f t r u n k ( 2 ) , h i n d l i m b ( _ ~ ) a n d f o r e l i m b ( , , ) . b : D a t a f r o m s i n g l e s u b j e c t i l l u s tr a t i n g p a r t ia l o v e r l a po f s e n s o r y a n d m o t o r r e p r e s e n t a t i o n s o f fo r e l i m b . F i l le d s y m b o l s i n d i c a t e s it e s w h e r e m o v e m e n t sw e r e e v o k e d b y 3 0 0 - H z s t i m u l u s ; o p e n s y m b o l s i n d i c a t e s e n s o r y r e s p o n s e :s t o t a c t il e s ti m u l i : h a l f -f i ll e d s y m b o l s s h o w s i te s w i t h b o t h p r o p e r t i e s . S y m b o l s a s i n 'a " p h i s v i b r i ss a e ( ~ ' ) , j a w ( ~ ) a n dc h e e k ( * ) . X s ( ) i n d i c a t e si t e s w h e r e s e n s o r y r e s p o n s e s t o l i g h t t a c t i le s t i m u l i c o u l d n o t b e f o u n d ,b u t t h e s e s i te s w e r e n o t s t i m u l a t e d t o t e s t f o r m o t o r r e s p o n s e s .


11/16

M O T O R A N D S O M A T O S E N S O R Y C O R T E X I N R A T ~:,-:

t h e s e a r e a s s e e m s n e g l ig i b le i n v i e w o f t h e f a c t th a t t h e d a t a w e r e c o m p i l e d f r o m1 6 r a ts . W i t h i n t h e l i m i t s o f t h e 0 .5 m m s p a c i n g o f e l e c t r o d e p e n e t r a t i o n s t h e r e w a sn o i n d i c a t io n i n d a t a f r o m i n d iv i d u a l a n i m a l s o f o v e r l a p in t h e r e p r e s e n t a t io n s o fd i s t in c t i v e l y d i f f e re n t p a r t s o f t h e b o d y . D i s t a l p o r t i o n s o f b o t h l i m b s w e r e r e p r e s e n t e din a n t e r i o r p o r t i o n s o f th e i r r e s p ec t iv e a r ea s , w i t h a n o r d e r l y p r o g r e s s i o n t o m o r ep r o x i m a l m u s c l e s i n p o s t e r i o r p o r t i o n s . P o i n t s r e p r e s e n t i n g t h e t r u n k in F i g. 7 a iz~-c l u d e s i te s r e s p o n s i v e t o s t im u l a t i o n o f th e t a il o n t h e p o s t e r o m e d i a l e d g e o f t h e a r e a .o f th e b a c k a n d d o r s a l n e c k a l o n g t h e p o s t e r i o r b o r d e r , a n d o f c h e s t a n d s h o u l d e ra l o n g t h e l a t er a l b o r d e r o f th e h i n d l i m b a r e a . A t l e as t h a l f o f th e h i n d l i m b a r e ai s b o r d e r e d l a t e ra l l y b y t h e t r u n k w h i c h i n t e rj e c ts b e t w e e n t h e l i m b s e x c e p t in l h ea n t e r i o r h i n d l i m b r e g i o n .

T o b e s u re t h a t t h e o v e r l a p o f s e n s o r y a n d m o t o r a r e a s w a s n o t a n a r t if a c t o t'p o o l i n g s e n s o r y a n d m o t o r d a t a f r o m d i f f e r e n t a n i m a l s f o r e l i m b o r h i n d l i m b a r e a sw e r e m a p p e d in b o t h w a y s i n 5 r at s. O n e e x p e r i m e n t o n t h e f o r e l i m b r e p r e s e n t a t i o n sis s u m m a r i z e d i n F i g . 7b . T h e a n t e r o m e d i a l p a r t o f t he s e n s o r y a r e a y i e ld e d f o r e l im bm o v e m e n t s w h e n s t i m u l a t e d e l ec tr ic a ll y . T h e s e n s o r y r e p r e s e n t a t i o n d i d n o t e n c r o a c hu p o n t h e m o r e m e d i a l a n d a n t e r i o r p a r t s o f t h e f o r e l i m b m o t o r a r e a . T h e m o t o r a r e ad i d n o t e x t e n d a s p o s t e r i o r l y o r a s l a t e r a l l y a s t h e f o r e l i m b s e n s o r y a r e a . T h e c o r t i c a lp o t e n t i a l s e v o k e d b y t a c t il e s t i m u l a t i o n i n t h es e e x p e r i m e n t s , a s w e l t as i n t h e e a r li e ro n e s c o n c e r n e d w i th j u s t t h e s e n s o r y a r e a , w e r e u s u a l l y f o u n d i n t h e m o s t s u p e r f ic i a l0 . 5 m m o f c o r t e x w h e r e i t i s g e n e r a l l y e a s i e r t o i s o l a t e s i n g l e u n i t s . E l e c t r i c a l s t i m u -l a t i o n i n t h e r e g i o n s o f o v e r l a p w a s c a r r i e d o u t o n l y a t a d e p t h o f 1 .5 m m i n o r d e r toe x p e d i te t h e e x p e r i m e n t s . A l l o f o u r p r e v i o u s e x p e r ie n c e i n d ic a t e d t h a t m o v e m e n tt h r e s h o l d s s h o u l d b e lo w a t t h a t d e p t h . M o v e m e n t s w i t h th r e s h o l d s h i g h e r t h a n 1 50/~ A w e r e n o t t a k e n t o i n d i c a t e a c o r t i c a l m o t o r a r e a . T h r e s h o l d s i n t h e r e g i o n s ~ ,fo v e r l a p w e r e c o m p a r a b l e to t h o s e in o t h e r m o t o r a r e a s , a v e r a g i n g a p p r o x i m a t e l y7 5 # A in th e s e e x p e r i m e n t s .

S i m i l a r i n v e s t i g a t io n s o f t h e h i n d l i m b a r e a v e r i f ie d th e v i r t u a l ly c o m p l e t eo v e r l a p o f s e n s o r y a n d m o t o r a r e a s n o t e d a b o v e . I n t w o e x p e r im e n t s , h o w e v e r ,h i n d l i m b m o v e m e n t s w e r e e v o k e d b y s t im u l a t i o n o f o n e o r tw o l o c a t i o n s in th e m o s ta n t e r i o r p a r t o f th e h i n d l i m b m o t o r a r e a w h e r e s e n s o r y r e s p o n s e s t o s t im u l a t io n o ft h e l im b c o u l d n o t b e f o u n d . T h i s r a is e s t h e p o s s i b i l i ty t h a t s e n s o r y a n d m o t o r a r ea ,sa r e n o t c o m p l e t e l y c o e x te n s iv e , b u t t h a t a n a r r o w a n t e r i o r b o r d e r r e g i o n m a y b er e g a r d e d m o r e a p p r o p r i a t e l y a s m o t o r .

N o c o r t ic a l r e s p o n s e s t o s t i m u l a t i o n o f th e c o r n e a w e r e o b s e r v e d i n t h e see x p e r i m e n t s , i n s p i te o f a n i n t e n s i v e s e a r c h f o r t h e m i n th e r e g i o n o f th e e y e l id p r o -j e c t io n s i n s e v e r a l e x p e r i m e n t s . T h e 0 . 5 - m m s a m p l i n g i n t e rv a l w a s n o t a d h e r e d t o i nt h e se e x p e r i m e n t s ; m a n y p e n e t r a t i o n s w e r e m a d e i n a n d a r o u n d t h e re l a ti v e ly s m a l le y e l i d r e p r e s e n t a t i o n s .D I S C U S S I O N

T w o m a p s o f t h e r a t 's m o t o r c o r t e x w e r e p r e s e n t e d b a s e d o n s t im u l i t h a td i ff e re d in f r e q u e n c y a n d d u r a t i o n . I t c o m e s a s n o s u r p r i se , o f c o u r s e, t h a t p a r a m -


12/16

34 R. D. HALL AND 1i. P. LINDHOL Me t e rs o f e l e ct ri c a l s t im u l i h a v e a p r o f o u n d i n fl u e n ce o n t h e r e s u lt s o f e x p e r i m e n t st h a t u s e s u c h s t i m u l a t i o n t o s t u d y t h e o r g a n i z a t i o n o f m o t o r c o r t e x 2~,2'5. A n d i t h a sb e e n k n o w n f o r s o m e t im e t h a t t h r e s h o l d s o f c o r ti c a ll y e v o k e d m o v e m e n t s , in c a t sa n d p r i m a t e s a t le a s t, d e p e n d o n t h e f r e q u e n c y o f b o t h s i n u s o i d a l a n d s q u a r e p u l s es t i m u l a t i o n 25. I n t h e p r e s e n t e x p e r i m e n t s t h r e s h o l d c u r r e n t s w e r e c o n s i s t e n t ly l o w e rf o r th e 3 0 0 - H z s t i m u l u s t h a n f o r th e l - k H z s t i m u l u s : b u t i t s e e m s u n l i ke l y t h a t t h el a r g e r a r e a d e l i m i t e d w i t h t h e 3 0 0 - H z s t i m u l u s r e f l e c t s t h e s m a l l t h r e s h o l d d i f f e r e n c e ,a p p r o x i m a t e l y 2 5 / ~ A . T h i s w a s m o r e t h a n c o m p e n s a t e d f o r b y t h e 50 -/~ A d if f e re n c ei n t h r e s h o l d c r i te r i a u s e d f o r a c c e p t in g r e s p o n s e s e v o k e d b y t h e t w o k i n d s o f s t im u -l a t io n . N o r is i t l i k e ly t h a t i ts s h o r t d u r a t i o n w a s r e s p o n s i b l e f o r t h e i n e ff i c ac y o f t h e1 - k H z s t i m u l u s i n th e d o r s a l a n d l a t e r a l p o l a r r e g i o n s . W e f o u n d , a s o t h e r s 3 ,7 ,1 sh a v e , t h a t h i g h f r e q u e n c y s t im u l i , 1 k H z o r h i g h e r , e v o k e b r i e f f li c ks a t th e o n s e t o ft h e s t i m u l u s t r a i n . L e n g t h e n i n g t h e t r a i n h a s l i tt le e f fe c t o n t h e r e s p o n s e o r i ts th r e s h -o l d .

T h e e f f e ct s o f l - k H z s i n u s o i d a l s t i m u l a t i o n r e s e m b l e t h o s e o f s i n gl e c a t h o d a lp u l s e s a p p l i e d t o t h e c o r t i c a l s u r f a c e l v a g . T o a c c o u n t f o r t h e l i m i te d v a r i e t y o f m o v e -m e n t s e v o k e d b y s i n g le c a t h o d a l p u l s e s i n th e b a b o o n k i d d e l l a n d P h i ll ip s 17 p r o p o s e dt h a t s o m e m u s c l e s a r e m o r e a c c e s si b le to c o r t ic a l s t i m u l a t i o n t h a n o t h e r s b e c a u s em o r e c o r ti c o f u g a l f ib e r s p r o j e c t t o w a r d s t h e m . T h e 1 - k H z m a p p r e s e n t e d h e r e m a yb e l a rg e l y a r e f le c t io n o f t h e m u s c l e s m o s t a c c e s s ib l e t o s t i m u l a t i o n o f t h e r a t ' sc o r t e x , t h o s e o f t h e v i b ri s s a e, f o r e l i m b a n d h i n d l i m b b e i n g s o c o n s p i c u o u s . T h e l a rg ep o r t i o n o f m o t o r c o r t e x d e v o t e d t o t h e m y s t a c i a l v i b r is s a e ( 20 ,~ o f t h e 3 3 s q . m mi n c lu d e d i n t h e m o t o r a r e a o f F ig . 6) is c o m p a r a b l e t o th e r e p r e s e n t a t i o n o f t h e v i-b r i s s a e in s o m a t o s e n s o r y c o r t e x , r e p o r t e d a s 2 0 ~ o f S m l b y W e l k e r ''~).

C y t o a r c h i t e c t o n i c d i v i s io n s o f t h e r a t ' s c o r t e x 5 a d o n o t s u g g e s t a n y a n a t o m i c a lb a s i s f o r th e d i s t i n c ti o n b e t w e e n t h e m o t o r a r e a s d e l i m i te d w i t h th e I - k H z a n d 3 0 0 - H zs t im u l i , n o r d o t h e y p r o v i d e a p i c tu r e o f a u n i f o r m s t r u c t u r e o f e i t h e r m o t o r a r e a .T h e l a r g e r a r e a o b t a i n e d w i t h th e 3 0 0 - H z s t i m u l u s i n c l u d e s a r e a s 4 , 6 , 8 a n d 1 0 inK r i e g ' s l c l a s si f ic a t io n a n d f , f ' a n d n i n t h a t o f D r o o g l e e v e r F o r t u y n a, b u t i t d o e s n o td i f fe r in t h i s r e s p e c t f r o m e a r li e r d e l in e a t i o n s o f t h e r a t ' s m o t o r c o r te x . O u r m a i nc o n c e r n h a s b e e n w i t h t h e f u n c t i o n a l o r g a n i z a t i o n o f th e m o t o r a r e a a s th i s is s e enw i t h e l e c tr o p h y s i o l o g i c a l t e c h n i q u e s , b u t t h e r e i s c l e a r ly a n e e d t o d e t e r m i n e t h es t r u c t u r a l b a s i s f o r t h is o r g a n i z a t i o n , i n c lu d i n g t h e c el l p o p u l a t i o n s i n v o l v e d i nc o r t i c a ll y el ic i te d m o v e m e n t s . I t w a s a c o n s i d e r a b l e a d v a n t a g e t o l e a r n t h a t t h e l o w e s tt h r e s h o l d s f o r s u c h m o v e m e n t s a r e to b e fo u n d r a t h e r d e e p i n th e c o r t e x , a n d t h i s a tl e as t s u g g e s ts t h a t d i r e c t s t i m u l a t i o n o f c o r ti c a l e f fe r e n t s m a y b e i m p o r t a n t . B u t t h et y p e o f e l e c t r o d e t h a t w a s u s ed , i m p r e c i s i o n s t h a t it i m p o s e s o n d e p t h m e a s u r e m e n t s ,a n d t h e l ac k o f a n y h i s to l o g i c a l in f o r m a t i o n a b o u t t h e s i te s o f s t im u l a t i o n m a k e i td i ff ic u lt t o s a y m u c h a b o u t t h e c o r t ic a l m e c h a n i s m s i n v o l v e d i n t h e m o v e m e n t s .T h e r e a r e , h o w e v e r , a n a t o m i c a l d a t a t h a t s u g g e s t s t r u c t u r a l b a s e s f o r t h e o v e r l a pb e t w e e n s e n s o r y a n d m o t o r a r e a s a n d f o r th e e ye e y el id m o t o r r e p r e s e n t a ti o n f o u n din t h e p r e s e n t e x p e r i m e n t s . T h e s e s p e c u l a t iv e r e l a t io n s h i p s a r e d i s c u s s e d i n t h e p a r a -g r a p h s t h a t f o l l o w .

T h e p r e s e n t d e l i n e a t io n o f S m l is i n g o o d a g r e e m e n t w i th W e l k e r ' s r e c e n t d e -


13/16

M O T O R A N D S O M A T O S E N S O R Y C O R T E X I N R A T - ~

s c r i p ti o n 29, a l t h o u g h o u r i n v e s t ig a t i o n o f th e h e a d a r e a w a s n o t n e a r ly a s t h o r o u g ha s h e r s . O f p a r t i c u l a r i n t e r e s t is W e l k e r ' s f in d i n g t h a t S m I d e f in e d b y e l e c t ro p h y s i o ~l o g i c a l c r i t e ri a c o i n c i d e d w i t h a c y t o a r c h i t e c t u r a l a r e a w i t h a p r o m i n e n t g r a n u l a rl a y e r I V . T h e o v e r l a p o f s e n s o r y a n d m o t o r a r e a s d e s c r ib e d a b o v e s u g g e s ts a n o v e r l a po f s e n s o r y g r a n u l a r a n d m o t o r a g r a n u l a r c o r t e x . A p o s s i b l e st r u c t u r a l b a s is f o r th i so v e r l a p i s K r i e g ' s a r e a 4 , i f t h e h i n d l i m b a r e a d e l i m i t e d h e r e . p l u s a p a r t o f t h e f o r e -l i m b r e p r e s e n t a t i o n , is e q u i v a l e n t t o t h a t a r e a , w h i c h i t s e e m s to b e . K r i e g t l r e g a r d e dt h is a r e a a s t h e h o m o l o g o f p r e c e n tr a l m o t o r c o r t e x i n p r i m a t e s b e c a u s e o f i ts l a rg ep y r a m i d a l c e ll s, it s h e a v y p r o j e c t i o n t o t h e b r a i n s t e m . a n d i ts p r o x i m i t y t o p a r i e ta ls e n s o r y c o r te x . B u t la y e r I V w a s a l s o f o u n d t o b e m o r e d e v e l o p e d t h a n i n t h e o t h e rf r o n t a l m o t o r a r e a s , 6 , 8 , a n d 1 0, e n o u g h s o t h a t K r i e g 11 s u g g e s t e d t h a t i n lo w e~f o r m s a r e a 4 m i g h t r e c e iv e d i r e c t s e n s o r y c o ll a te r a ls . D r o o g l e e v e r F o r t u y n ' s a r e a n .w h i c h s e e m s r o u g h l y c o m p a r a b l e t o K r i e g ' s a re a 4 . w a s a l so d e s c r ib e d a s t h e a r e aw i t h t h e l a r g e s t p y r a m i d a l c e ll s a n d a w e l l d e v e l o p e d l a y e r I V . W e l k e r 29, i t m i g h t b en o t e d , c a l le d a t t e n t i o n t o l a r g e p y r a m i d a l c e l ls i n l a y e r V b i n th e m e d i a l p a r t o fh e r S m I , w h i c h is p o s s i b l y e q u i v a l e n t t o K r i e g ' s a re a 4 . T h i s k i n d o f o v e r l a p o [c y t o a r c h i t e c t u r a l c h a r a c t e r i s t i c s h a s b e e n f o u n d f o r t h e e n t i r e s e n s o r i m o t o r p a r i e t a lc o r t e x o f t h e o p o s s u m b y W a l s h a n d E b n e r zs . w h i c h a g r e e s n i c e ly w i t h L e n d e ' s 1~f in d i n g o f a c o m p l e t e o v e r l a p o f s o m a t o s e n s o r y a n d m o t o r a r e a s in th i s sp e c ie s asd e t e r m i n e d w i th e l e c tr o p h y s i o l o g i c a l m e t h o d s . C o m p l e t e l y o v e r l a p p i n g t h a l a m i cp r o j e c t io n s f r o m t h e v e n t ra l p o s t e r i o r a n d v e n t r a l a n t e r o la t e r a l n u c l ei in t h e o p o s s u mf u r t h e r a t te s t t o th e o v e r l a p o f s e n s o r y a n d m o t o r a r e a s s. U n f o r t u n a t e l y , c o m p a r a b l ep r o j e c t i o n s t o a r e a 4 w e r e n o t f o u n d b y K r i e g 1-, b u t t h e f a c t th a t h e f o u n d n o t h a l a m i cp r o j e c t i o n t o a r e a 4 s u g g e s t s t h e p o s s i b i l it y th a t t h e p r o j e c t i o n s w e r e m i s s e d f o r s o m er e a s o n . K r i e g 9 h a s p l a c e d a r e a 4 a b o u t I m m m o r e a n t e r i o r t h a n t h e h i n d l im b a r e ad e l i m i t e d h e r e ; b u t a t t h e v e r y le a s t th e r e w o u l d h a v e t o b e a p p r e c i a b l e o v e r l a p b e--t w e e n t h e t w o , a n d i t s e e m s m o r e l ik e ly t h a t t h e r e i s s o m e e r r o r i n t h e c o o r d i n a t e sr a t h e r t h a n a d i f f e r e n c e b e t w e e n t h e t w o a r e a s .

T h e e x t e n s i v e r e p r e s e n t a t i o n o f e y e a n d e y e l i d m u s c l e s a l o n g a t h i n s t r i p o f c o r te xn e a r t h e m i d l i n e w a s n o t a n t i c i p a t e d o n t h e b a s i s o f e a r l i e r s t u d i e s o f t h e r a t ' s m o t o rc o rt ex a 3, 21 , 23. L e o n a r d 15, h o w e v e r , f o u n d a r e g i o n o f c o r t e x a l o n g t h e d o r s o m e d i a ls h o u l d e r , a n t e r i o r a n d d o r s a l t o th e g e n u o f t h e c o r p u s c a l l o s u m , w h o s e c o n n e c t i o n sc l o se l y r e s e m b l e th o s e o f t h e fr o n t a l e y ef ie ld s in t h e m o n k e y , B r o d m a n n ' s a r e a 8 .T h i s s h o u l d e r r e g i o n i n th e r a t r e c e iv e s f i b e rs f r o m t h e d o r s a l m e d i a l n u c l e u s o ft h e t h a l a m u s a n d p r o j e c t s to t h e p r e t e c t u m a n d s u p e r i o r c o ll ic u l u s , a s w e ll a s p a r a -m e d i a n m e s e n c e p h a t i c s tr u c t u r e s a n d d o r s a l m e d i a l n u c le u s . I t s e e m s t o c o r r e s p o n dt o t h e e y e - e y e l i d a r e a d e l i m i t e d i n t h e p r e s e n t s t u d y e x c e p t t h a t i t d o e s n o t e x t e n d a sf a r c a u d a l l y . D r o o g l e e v e r F o r t u y n 5 a n d K r i e g 12 b o t h d i s ti n g u i sh e d t h is s h o u l d e rr e g i o n , a r e a s f ' a n d 1 0 a r e s p e c t i v e l y , f r o m t h e l a t e r a l l y a d j a c e n t f r o n t a l a r e a s , b u ti t i s n o t c l e a r t h a t t h e se a r e a s c o r r e s p o n d m o r e c l o s el y to t h e e y e - e y e l i d a r e a f o u n dh e r e th a n L e o n a r d ' s s h o u l d e r r e g i o n d o es . W e c a n n o t r u l e o u t t h e p o s si b il i t y th a t t h ee y e o r e y e li d m o v e m e n t s w e r e e v o k e d f r o m t h e c in g u l a t e c o r te x d e s c r ib e d b y D o m e -s i c k 4 , w h i c h l ie s a d j a c e n t t o L e o n a r d ' s s h o u l d e r r e g i o n a n d a l s o p r o j e c t s s u b s t a n t i a l l yt o t h e l o w e r I a y e r s o f t h e s u p e r i o r c o l li c u lu s t h r o u g h o u t t h e l e n g th o f t h e c e r e b r u m .


14/16

36 R. D, HALL AND E. P. LINDHOLMR e s o l u t i o n o f t h is q u e s t i o n a n d o f th o s e p e r t a i n i n g t o t h e r e g i o n o f o v e r l a p b e t w e e ns e n s o r y a n d m o t o r a r e a s s h o u l d b e p o s s ib l e w i t h t h e p r e c is e l o c a l iz a t io n o f st im u -l a t io n a n d r e c o r d i n g s it es b y h i s t o l o g i c al t e c h n i q u e s i n f u t u r e e x p e r i m e n t s .

T h e f i n d i n g t h a t e y e l id m o v e m e n t s w e r e n e v e r c l o s u r e s w a s a n u n e x p e c t e d f in d -i ng , f o r e y e l id m o v e m e n t s e l ic i te d b y c o r t i c a l s t i m u l a t i o n i n v a r i o u s s p e ci es h a v en e a r l y a l w a y s b e e n d e s c r i b e d a s c l o s u r e s . O n e e x c e p t i o n i s t h e w i d e n i n g o f t h e p a l -p e b r a l f is s u re t h a t i s p a r t o f a d v e r s iv e e y e m o v e m e n t s f o u n d w i th s t i m u l a t i o n o ff r o n t a l c o r t e x i n m a n a n d m o n k e y 20. T h e c l o se a s s o c i a t i o n o f e y e a n d e y e l id a r e a s i nt h e r a t , a s in p r i m a t e s ~7, a n d t h e f a c t t h a t e y e a n d e y e l i d m o v e m e n t s s o f r e q u e n t l yo c c u r r e d t o g e t h e r i n t h e p r e s e n t e x p e r i m e n t s s u g g e s t t h a t s o m e e y e li d o p e n i n g s s e e nh e r e w e r e li ke th o s e o f a d v e r s iv e e y e m o v e m e n t s . O t h e r o b s e r v a t i o n s s u g g e s t t h a ts o m e s m a l l o p e n i n g s a r e r e al ly i n c ip i e n t cl o s u r es . M e a s u r e m e n t s o f e y el id m o v e m e n t si n u n a n e s t h e t i z e d r a t s ( u n p u b l i s h e d o b s e r v a t i o n s ) h a v e s h o w n t h a t t h e i n i t i a l p a r t o fa b l i n k i s f r e q u e n t l y a w i d e n i n g o f t h e p a l p e b r a l f is s u re . T h e m o s t c o m p e l l i n g e v i -d e n c e t h a t t h e s m a l l o p e n i n g m a y b e a n i n c i p i e n t c l o s u r e w a s f o u n d i n o n e o f t h e p r e s-e n t e x p e r i m e n t s i n w h i c h i t w a s p o s s i b l e t o e li c it f u l l a n d s u s t a i n e d c l o s u r e s o f t h el i d s b y s t i m u l a t i n g a p o i n t i n S m I w h e r e c e l l s r e s p o n d e d t o t a c t i l e s t i m u l a t i o n o ft h e l i d s. B y r e d u c i n g t h e i n t e n s i t y o f t h e c o r t i c a l s t i m u l u s i t w a s p o s s i b l e t o c o n t r o lt h e a m o u n t o f cl o s u r e . A t t h e l o w e s t in t e n si ti e s th e c l o s u r e w a s t r a n s f o r m e d i n t o as l i g h t o p e n i n g t h a t r e s e m b l e d t h e e y e l i d m o v e m e n t s s e e n t h r o u g h o u t t h i s s t u d y w i t hs t i m u l a t i o n o f m o t o r c o r t e x . S t il l a n o t h e r p o s s i b i li t y , f o r t h e u p p e r e y e l i d a t l e as t ,is t h a t t h e r a i s in g o f th e l id r e s u l t e d f r o m a c t i v a t i o n o f M f i l l e r 's m u s c l e t h r o u g h s t i m -u l a t io n o f c o r t e x s e rv i n g a u t o n o m i c fu n c t i o n s . B u t t h i s w o u l d n o t a c c o u n t f o r t h ef a c t t h a t o n l y t h e s a m e k i n d o f m o v e m e n t w a s s e en in t h e l o w e r l i d, b e c a u s e n os m o o t h m u s c l e is p r e s e n t , a p p a r e n t l y , i n t h e r a t ' s l o w e r l i d 2~.

T h e c l a ss ic p i c t u r e 3 o f s e n s o r y a n d m o t o r ' h o m u n c u l i ' l y in g o p p o s e d a s m i r r o ri m a g e s o n t h e a n t e r i o r c o r t e x o f t h e r a t r e m a i n s u s e f u l as a r o u g h g u i d e t o t h e o v e r a llo r g a n i z a t i o n o f th e s e a re a s , t h e p u r p o s e f o r w h i c h i t w a s i n t e n d e d . T h e v i r tu a l l yc o m p l e t e o v e r l a p o f h i n d l i m b r e p r e s e n t a t io n s , h o w e v e r , r e q u ir e s th a t t h e m i r r o ri m a g e s b e c o l la p s e d i n t o o n e i n t h a t r e g i o n , a n d t h e p a r t i a l o v e r l a p o f fo r e l i m b a r e a sr e q u i r e s a si m i l a r , b u t s m a l l e r a d j u s t m e n t . T h e l o n g t h i n s t r i p w h e r e e y e a n d e y e l i dm o v e m e n t s w e r e e v o k e d m a y n o t b e a n i n t e g ra l p a r t o f t h e 'p r e c e n t r a l ' m o t o r a r e a ,b u t a s p e c i a l i z e d re g i o n l ik e t h e f r o n t a l e y e f i e l d s o f p r i m a t e s , a s s u g g e s t e d a b o v e .B u t t h e r e g i o n s e e m s t o b e a p p r o p r i a t e l y p l a c e d t o f it i n w i th t h e g e n e r a l t o p o g r a p h i c a lo r g a n i z a t i o n , j o i n i n g t h e ' p r e c e n t r a l ' a r e a w h e r e t h e d o r s o l a t e r a l a s p e c t o f t h e h e a dis re p r e s e n t e d . T h e t w o r e g i o n s m a y b e i n t e g r a t e d i n a s in g le c o m p l e t e m o t o r s c h e m ei n w h i c h t h e e y e l i d m u s c l e s a r e r e p r e s e n t e d o n c e i n c l o s e a s s o c i a t i o n w i t h m u s c l e s o ft h e e y e .ACKNOWLEDGEMENTS

T h i s r e s e ar c h w as s u p p o r t e d b y N a t i o n a l i n s t i tu t e s o f H e a l t h G r a n t 5 P 01G M 14940-06.

W e a r e i n d e b t e d t o D r . C . N . W o o l s e y w h o g r a c i o u s l y p r o v i d e d u s w i th d e t a i ls


15/16

MOTOR AN D SOMATOSENSORY CORTEX IN RA I .~

o f h is e x p e r i m e n t a l p r o t o c o l s , t o W . W e l k e r f o r s e v e r a l h e l p fu l s u g g e s t i o n s , t o C . M ~L e o n a r d f o r u n p u b l i s h e d o b s e r v a t i o n s o n th e c o r t i c o s p i n a l t r a c t , a n d t o V . B~D o m e s i c k f o r b e n e f i c i a l d i s c u s s i o n o f t h e r e s u l t s .

R E F E R E N C E S1 A SA N UM A , H . , A ND S AK AT A , H . , F u n c t i o n a l o r g a n i z a t i o n o f a c o r t i c a l e f f e r e n t s y s t e m e x a m i n e d

w i t h f o c a l d e p t h s t i m u l a t i o n i n c a t s , J. Neurophysiol . , 3 0 ( 1 9 6 7 ) 3 5 - 5 4 .2 A S AN U M A , H . , S T ON E Y, S . D . , J R ., A N D A B ZU G , C . , R e la t ion sh ip be tw ee n a f f e r en t i npu t an d m ot o ro u t f l o w i n c a t m o t o r s e n s o r y c o r t e x , J . Neurophysiol . , 31 (1968) 670 -681 .

3 B R O W N , M . t . , A ND B RA C KE TT , C . E ., J R ., S ub cor t i ca l t h r e sh o ld vo l t ag es a s a fu nc t io n o f s in ew a v e f r e q u e n c i e s , J. Neurophysiol . , 21 (195 8) 279-291 .4 D O M ES lC K , V . B . , P ro j ec t io ns f rom the c in gu la t e co r t ex in t he r a t , Brain Research, 12 (1969) 296320 .5 D RO OG LE EVER FO RT U Y N, A . B ., O n the ce l l - l am ina t i on o f t he c e reb ra l co r t ex in som e rod en t s ,A rch . N euro l . P sych i a t . ( Lond . ) , 6 ( 1 9 1 4 ) 2 2 1 - 3 5 4 .6 E R IC KS ON , R . P ., N o n t r a u m a t i c h e a d h o l d e r s f o r m a m m a l s , Physiol . Behav. , 1 ( 1 9 6 6 ) 9 7 - 9 8 .

7 H IN E S, M . , M o v e m e n t s e l i ci te d f r o m p r e c e n t r a l g y r u s o f a d u l t c h i m p a n z e e s b y s t i m u l a t i o n w i t hs i n e w a v e c u r r e n t s , J. Neurophysiol . , 3 ( 1 9 4 0 ) 4 4 2 - 4 6 6 .8 K IL LA C KE Y, H . , A ND E B NE R , F . , C o n v e r g e n t p r o j e c t i o n o f t h r e e s e p a r a t e t h a l a m i c n u c l e i o n t ~a s i n g l e c o r t i c a l a r e a , Sc i ence , 1 7 9 ( 1 9 7 3 ) 2 8 3 - 2 8 5 .

9 K R IE 6 , W . J . S., A c c u r a t e p l a c e m e n t o f m i n u t e l e s i o n s i n t h e b r a i n o f t h e a l b i n o r a t , Quart . Bul l .Northw. Univ . med. Sch. , 2 0 ( 1 9 4 6 ) 1 9 9 - 2 0 8 .

1 0 K RI E G , W . J . S ., C o n n e c t i o n s o f t h e c e r e b r a l c o r t e x . 1 . T h e a l b i n o r a t . A . T o p o g r a p h y o f t h ec o r t i c a l a r e a s , J. comp. Neurol . , 8 4 ( 1 9 4 6 ) 2 2 1 - 2 7 5 .1 1 K R IE G , W . J . S . , C o n n e c t i o n s o f t h e c e r e b r a l c o r t e x . 1 . T h e a l b i n o r a t . B . S t r u c t u r e o f t h e c o r t i c a la r e a s , J . com p . N euro l . , 8 4 ( 1 9 4 6 ) 2 7 7 - 3 2 4 .1 2 K R IE G , W . J . S . , C o n n e c t i o n s o f t h e c e r e b r a l c o r t e x . I . T h e a l b i n o r a t . C . E x t r i n s i c c o n n e c t i o n s .J . com p . N euro l . , 8 6 ( 1 9 4 7 ) 2 6 7 - 3 9 4 .1 3 L AS HL EY , K . S . , S t u d i e s o f c e r e b r a l f u n c t i o n i n l e a r n i n g . I II . T h e m o t o r a r e a s , Brahe, 4 4 ( 1 9 2 l i2 5 5 - 2 8 5 .1 4 L EN DE , R . A . , A c o m p a r a t i v e a p p r o a c h t o t h e n e o c o r t e x : L o c a l i z a t i o n in m o n o t r e m e s , m a r s up i a l s a n d i n s e c t i v o r e s , A m t . N . Y . A c a d . S c i . , 167 (1969) 262 275 .1 5 L EO NA RD , C . M . , T h e p r e f r o n t a l c o r t e x o f t h e r a t . 1 . C o r t i c a l p r o j e c t i o n o f m e d i o d o r s a l n u c l e u sI 1 . E f f e r e n t c o n n e c t i o n s , Brain Research, 1 2 ( 1 9 6 9 ) 3 2 1 - 3 4 3 .16 LIBOUBAN-LETOUZE,S ., Etudes ~ lectrophysiologique des St ructures C~r~brales du Ra t B lanc, D o c -t o r a l t h e s i s , U n i v . P a r i s , 1 9 6 4 .17 LI D D E LL, E . G . T . , A ND P H ILLIP S , C . G . , T h e co r t i ca l r ep res en ta t io ns o f m oto r un i t s , Brain, 75(195 2) 5 10 -5 25 .18 LILLY , J . C . , A U S T IN , G . M . , A N D C HA M BE RS , W . W . , T hr esh o ld m o ve m en t s p rod uc ed by ex c i t a -t i o n o f c e r e b r a l c o r t e x a n d e f f e re n t f i b e r s w i t h s o m e p a r a m e t r i c r e g i o n s o f r e c t a n g u l a r c u r r e n tp u l se s ( c a ts a n d m o n k e y s ) , J. Neurophysiol . , 1 5 ( 1 9 52 ) 3 1 9 - 3 4 1 .1 9 L IV IN GS TO N , A . , A ND P H IL L IP S, C . G . , M a p s a n d t h r e s h o l d s f o r t h e s e n s o r i m o t o r c o r t e x o f t h ec a t , Quart . J . exp. Phys iol . , 4 2 ( 1 9 5 7 ) 1 9 0 - 2 0 5 .2 0 M E TT LE R, F . A . , S u p r a t e n t o r i a l m e c h a n i s m s i n f l u e n c in g th e o c u l o m o t o r a p p a r a t u s . I n M . B .BENDER (Ed. ) , The O cu l om ot or Sys t em , H a r p e r a n d R o w , N e w Y o r k , 1 9 6 4 , p p . 1 - 1 7 .2 1 O H T A , M . , C o r t i c a l m o t o r f u n c t i o n a n d t h e a n t i d r o m i c c o r t ic a l r e s p o n s e t o s t i m u l a t i o n o f t h em e d u l l a r y p y r a m i d a l t r a c t i n t h e r a t , Jap. J . Phys iol . , 18 (1968) 10 0 -124 .2 2 P H IL L IP S, C . G . , C h a n g i n g c o n c e p t s o f t h e p r e c e n t r a l m o t o r a r e a . I n J . C . EC CL ES ( E d . ) , BraiJ~and C onsc i ous E xper i ence , S p r i n g e r , N e w Y o r k , 1 9 66 , p p . 3 8 9 - 4 2 1 .23 SETTLAGE, P . H . , BINGHAM, W . G. , SUCKLE, H. M. , BORGE, A. F . , AND WOOLSEY, C . N. , Th e pa t-t e r n o f l o c a l i z a ti o n i n t h e m o t o r c o r t e x o f t h e r a t , Fed. Proc. , 8 (1949) 144 .24 STONEY, S . D . , JR ., THOMPSON, W . D. , AND ASANUMA, H. , Ex ci t a t i on o f py ra m id al t ra ct c el ls b vi n t r a c o r t i c a l m i c r o s t i m u l a t i o n : E f f ec t iv e e x t e n t o f s t i m u l a t i n g c u r r e n t , J. Neurophysiol . , 31 (1968)6 5 9 - 6 6 9 .25 T E RZU O LO , C . A . , A N D A D E Y , W . R . , S en so r im oto r co r t i ca l ac t iv i t i e s . I n J . F I E LD (E d . ) , H a n d b o o ko f Phys iolog y, I iol . H, A m e r . P h y s i o l . S o c . , W a s h i n g t o n , D . C . , 1 9 6 0 , p p . 7 9 7 - 8 3 5 .


16/16

3g R. D. HALL AND E. P. LINI)HOI.M26 TIL(iNIR, V. S., Anato mic der/:iusseren Augenmuskeln und des Ob erlidheb ers der Ratte (R~zltll.~

,orregiczl .r , Berkenhout 1769), A , a t . A r i z . , 125 (1969) 496-51 I.27 WA(;mAN, 1. H., Eye movements induced by electric stimulation of cerebrum in monkeys andtheir relat ionshi p to bodily m ovements. In M. B. BENDER (Ed.), The Oc ' t t lomotor S v,s'tem. Har perand Row, New York , 1964, pp. 18 39.28 WALSH, T. M., AND EBNER, F. F., The cytoarchitccturc of somatic sensory-motor cortex in theopossum ( DMelp/zi, r ~,arsHpiali, s' vi rg i, ia~la) : a Golgi study, J . A , o t . ( Lo* l( l. ), 107 (1970) I 18.29 WEt,KeR, C., Microelec trode delineation of fine grain so mat oto pic organiz_qtion of Sml neocorlexin albino rat, B r a i , R e s e a r c h , 26 {1971) 259 275.30 WOOLSEY, C. N., Patt erns o f local ization in sensory and mot or areas of cerebral cortex. In

M i l b a , k Me mo r i a l F t md , T h e Bi ol og .v o f Me Ht a l He a l t h a , d D i se a, ve , Hoeber, New York, 1952,pp. 193 206.

paw coordinate

Documents