Parietal Mechanisms of Visuomotor Behavior and Spatial Cognition

Carl Olson

1. Parietal cortex as a hub for crossmodal. and sensorimotor communication

2. Impact of parietal injury in humans

3. Area LIP and the transition from retina-centered to body-centered visual representations

4. Area VIP as a site of body-centered visual representations

5. Area MIP and the representation of arm movements in a retina-centered reference frame

6. Area AlP and the matching of grasp posture to object shape

Reading:

Spatial Cognition " Ch. 53 , Zigmond et al. (eds ), Fundamental Neuroscience, pp. 1363-1383.

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Fig. 3. Schematic diagram of the cortical visual areas in the macaque and their interconnections. Solid lines indicate projections in-volving all portions of the visual field representation in an area, whereas dotted lines indicate projections limited to the representationof the peripheral visual field. The connections between area V4 and PO are shown in both solid and dotted lines to indicate thatthe projection is heavier from the peripheral visual field. Heavy arrowheads indicate ' forward' projections, which terminatepredominantly in layer 4 , light arrowheads indicate ' backward' projections, which tend to avoid granular layer 4 and terminate in-stead in the supragranular and infragranular layers, and lines with two reciprocal arrowheads indicate intermediate projections (Tig-ges et aI. , 1973, 1974; Rockland and Pandya, 1979; Van Essen and MaunseU 1983; Ungerleider, 1985; Ungerleider and Desimone,1986). 'd' indicates that the projection from VI and V3 is limited to the dorsal portion of V3. ' ' indicates that the connectionsof VIP with both V2 and PO are limited to VIP' s medial portion. Adapted from Ungerleider and Desimone (1986).

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Even reaching for your coffee cup requires using visual information, proprioceptiveinformation and copies of motor signals to compute the cup s location in the workspacearound the body.

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Key points:

1. Parietal cortex, at the hub of the visual , somatosensory and motor systems , is ideallyplaced to mediate visually guided reaching and other f~rms of visuomotor guidance.

2. Visuomotor guidance is disrupted by parietal lesions in humans.

3. Neurons in different areas of monkey parietal cortex show signs of being involved insuccessive stages of the process by which the representation of retinal image location istransformed into a spatial representation useful to the motor system.

4. It appears that parietal mechanisms for the representation of space ramified over thecourse of evolution well beyond the domain of visuomotor guidance. Neuropsychologicalstudies in humans have revealed that high-order visuospatial functions without any motorcomponent depend on parietal cortex.

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TA8Lf 12. 2. Summary of major symptoms of parietal lobe damage

Symptom Most probable lesion site Basic reference

Disorders of tactile function Areas I. 2. 3 Semmes et aL. 1960Corkin et aL. 1970

Hecaen and Albert. 1978Brown. 1972

Heilman and Rothi. 1993Geschwind. 1975

Kimura. 1980

Tactile agnosia Area PE

Apraxia Areas PF. PG, left

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Disorders of spatial ability

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Defects in eye movement

Misreaching = of't, c ~ t Gl" \ ""

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Case description of a patient with impaired visuospatial cognitionCopying and drawing were poor and lacked perspective. Printing in uppercase letters was verydisorganized when he wrote looking at the page , but when blindfolded or when writing cursive he wasnot impaired. The difficulties of reading and writing in print were entirely derived from his inability tolocate letters and numbers on the page under visual control. Writing cursive with lowercase letters wasgood , since this does not require specifically visual positioning of each letter.

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Figure 5. Copying a star with matchsticks. Examples from and left- and right-hemi-sphere lesions IMcFie & Zangwill, 1960).

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Figure 5. Example of constructional failure on Koh's Blocks. , From Critchley, 195.

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Case 2. (Castaigne, Pertuiset , Rondot and de Recondo, 1971.) M. M. A. , aged. 36, mother of twochildren , previously in good health , was admitted in November 1969 for a meningeal syndrome ofsudden onset. The diagnosis of subarachnoid h~morrhage was confirmed by lumbar puncture.

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During the following months, she complained of difficult, in ras in ob'ec s her I . Similarly,hen she w~~~a!i!1.8m~als she could ea~U)' t~~e L~_ ~I)Q~_ofth~J~y~n,gI'-.anj!.!.t.:vas turned to the

ight but she often di~IWtif ilpointecUojhe .~JJ~- ~04~he_said.J she saw it These-difficuHieswere ked to the presence ora vi suo motor ataxia localized in the left visual field. This was characterizedby marked difficulty in grasping objects presented in the left visual field. The patient , moreover

oj the ob~~a ~-i~tilncefroE1 i~ real position , usua~ ~1:!1~~t she explor~ space like a ind l!'If she knocked against the arm oftheexaminer or the object , correction was immediate and she graspedthe object. The disorder was present whatever the object presented , its nature , form , colour and atwhatewr distance it was placed from the subject. It affected only the left visual field; while graspingobjects was perfect when presented in the right lateral field , the gesture was hesitant unco-ordinatedaitdc1umsy and the subjecl could not grasp the object when presented in the left lateral field. Thisanomaly existed in the temporal field of the left eye and the nasal field of the right eye.

This difficulty in grasping objects was only obser~~d in lateral vision t~~t jSt~, ~!?.hep'(ltie I'?okin!!?.~t ~f her and an obje,:t~:!l P!~~!2t.e~_ tn the leftJj.eldJp~ed, it disap~red complete!l)fthe ~jec\\i!~Jhed-L-!JKgestuLe.Jhen...Q.eing P!~i~ al!~ ra'pi~- e,-,~ Jr.~~~~oa! t~~~~_ taj~e~ \\'a~ si!uat~i().!1 theIeft

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I~r returning to lateral vision. she executed more easily the order given. Performance was even betterii" one first asked that the object he fixed and then the latter was moved causing an ocular pursuit mon~-m~nt. Thus. fixation of the object overcomes the disorder and previous fixation improves it even if thepatient is no longer fixing the object when performing the movement.

Th~.Ali9.r.Qer in left la eral vision was~l)j.i~!l, whether the riwht or left hand was used . When the

, object was presented i e r t lateral field the movement was as prec se r the right hand as forIh~ left. In this way. if instead of presenting an object. the subject was asked to grasp her own handpassively placed in her left hemi-field at variable distances. the movement was always precise and adept.t was also p'r~ise i~he was asked to touch with her left or ril!~erent parts of her body on thegh~ pr left.

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FIG. 4. Distribution of the spatial errors across the different hand.field combinations for each right-damaged(A) and each left-damaged (B) patient, and for the control group (c) during reaching at a visual object. Thenumber of errors is given as the percentage of the total number of trials for each combination and eacb subject.\\-'bite bars = corrected errors; hatched bars = noncorrected errors. L YF = left visual field; CYF = central visualfield; R YF = right visual field. Note that in both groups of patients there is a 'visual field effect' (i. , err~rswith both hands in the field contralateral to the lesion). In tbe left-damaged group (Case 10 excepted) there isan additional 'hand effect ' (i. , errors with tbe right hand not only in tbe rigbt hemifield but also in the lefthemifield and in 3 patients also in tbe central field).

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Saccade OnsetFig. 2. Response of an LIP neuron in a remembered saccade task. The cartoon above each diagram shows the relative locations of the fIXation point (FP)and the receptive field (RF). The time lines show vertical eye position (V) and the onset and offset of a stimulus in the RF. Each tick mark in the rasterdiagram signifies a single action potential. Successive trials are shown on successive lines, synchronized (vertical line) on the event indicated below thehistogram. The calibration bar at left signifies a response rate of 100 spikes/so In this task, the monkey must fixate while a stimulus is briefly presented inthe RF. After a variable delay, the fIXation point is extinguished and the monkey saccades to the location where the stimulus appeared. Separate visual andmotor bursts are seen in each trial, as well as tonic activity during the memory period.

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figure 2. a, Structure of the Mixed ~.P network. The network is composed of threelayers of computing units: input units lencoding retinal location of stimulus and eye

positionl. hidden units. and output units lencoding head-centered location of the visualstimulusl. Retinal position of the visual stimulus is eocoded topographically by an 8x 8 array of input units, each with a gaussian receptive field Idescribed in bl. Theremaining 32 input units code for eye position in a linear fashion lsee c/. with two

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and two groups of eight units for venical angle. Units in the. outpUt layer code forhead-centered coordinates in a monotonic format

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loutput 21 similar to the retinal input. The hidden unitsare binary stochastic elements. while the output units are deterministic logistic elements

Isee Fig. 31. Shading is proponional to unit activity in the input and output layers.Connection weights are indicated by w. b, Angle-coding function of the retinal inputunits. Each unit's aCtivity level is a gaussian function of the retinotopic J- and)'COOrdinates of the visual stimulus. one 1/ e width of 150. and spaced 100 apanfrom that of its neighboring units. c, Angle-coding function for the eye position units.

Each unit codes for the or eye position linearly. The slopes and intercepts foreach unit were assigned randomly within ranges observed for area 7a neurons.

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JC. OIdjtut; the rest used the pussian fonnat output.

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Figure 2 Single-neuron data for visual receptive field mappings in which the RF

remains in the same spatial location irrespective of eye position. The RF was

mapped with a white bar moving at 100 deg S 1 for brief intervals in the neuron

preferred direction. a, Colour-coded maps of the RF were constructed for each

fixation position. Contour maps represent isofrequency intervals computed from

linearly interpolated data matrices, Maps are displayed in screen coordinates,The small white crosses correspond to the eye position during visual stimulation;

the intersection of the light horizontal and vertical lines corresponds to thestraight-ahead direction in space. b , Contour plots forthe top left, top right. bottomleft and bottom right RF maps show the stimulation region from which firing rates

above 50% of peak discharge were obtained, The left graph superimposes thefour RF maps as they appear in screen coordinates (as in the colour-coded plots);

the right graph represents the same maps but reframed in eye coordinates(relative to the fovea).

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. FIgure 1 Responses of 0. (" e.o..~ '" +SpeCiftc neuron in the deIayed-saccade(left) and delayed-reach (right) tasJcs. Each panel shows timing of peripheral flashCue' : red flashes indicated by filed bars, green flashes by open bars) and

response ('Saccade' or ' Reach' t eight rows of rasters corresponding to f!Ne(ythird action potential recorded during each of eight trials: 8 spike densityhistogram of neuronal ac1Mty, genend8d by conYOIution with a triangular kerneJ27aligned on cue presentation, wtIh cue onset and offset indicated by dashed lines:

and eight over1aid traces showing YerticaI eye position. Neuronal responses inthe cue interval (50 ms before to 150 ms after cue offset) were nonspecificHoweYer, during the delay interval (15O-Emma), tiring depended specificallyon motor intent

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Rgure 1 Visuomotor transformation schemes. 3 , Example of reaching for a cup while

fixating on a newspaper. The position of the cup is initially represented in the brain in

terms of ITS iocation on the peripheral retina (T). To reach for the cup, its posITion with

respect to the hand must be known (M). This information couid be acquired by directly

subtracting hand position (H) from target position (T) in eye coordinates (3, b), or by

gradually transforming the position of the target from eye- to body-centred coordinates,

and subtracting the body-centred position of the hand (c). (Adapted from ref. 29.

Condition 1 Condition 3

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Rgure 2 Responses of a single neuron from area 5. 3, Diagram of a macaque monkey

brain showing the location of area 5 (shaded region) and the approximate location of the

magnetic resonance image (MRI) section in b. ips, intraparietal sulcus. b, Coronal T1-

weighted MRi section through the approximate centre of the area 5 recording sites. Scale

bar, 1 em, c , Spike density histograms of the activity of one area 5 neuron for the same

planned movement vector (down and to the right) in each of four experimental conditions.

Vertical scale bar, 140spikess \ horizontal scale bar, 1 s.

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INIT. ~~.=::::IfiIIn 1. A. The experimental setup and time sequence of manipulation task. L/, fixation spot; l.2. a small LED attached on top of each object KEY. an anchor key at lap level; Sw.. IIIicroswiIch connected 10 the object In tha time sequence chart, upward deflection of traces in both 11 and L2 indicates red 1m or green 16; hatched ",,1 LED color. Upwardd8IIec1ion of traces in KEY and SW denotes the time during which tha key was pressed and the switch was held on. S, The four types of objects for manipulation and the shape .of monkey's h~nd. See further details in the text.

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104

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Figure 5. Results of principal components extraction. ~) The SVD ar8ysis showed two factors.

Factor 1 accounts for 77.5% of variaoce of al the data. (8) The main factor is related to the difference between the grasping tasIc (6) and the matcli~

~.

jC) The POsitive corresponds mainly to tile ~I ::: III the !Irasoing tas~(0) The neaative !!!Jage shoWstfte network IIIYO/Yed iii matching task. The eigenimages are as a maxinun IIItensity projeCtion 111 format The color scaleis arbitrary and eaCnlmage is scaled to its 1TIiIXIII1U/I'I. numbers il1licate the size in mm of the stereotactic box. R irdcates the right hemisphere. VAt and VfC are the verticalstraversing the anterior and posterior commissures.

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..... 1. Object shapes used in the tasks. Eadt shape was buit in tine sizes.

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