1 jhu bme 580.422 biological systems ii adaptation of visuomotor maps disorders of parietal cortex...
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JHU BME 580.422 Biological Systems II
Adaptation of Visuomotor Maps
Disorders of parietal cortex
Reza Shadmehr
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xh
Proprioceptive state of the body: arm, head, and eye positions
xt
xa q fq
hand location in fixation coordinates
Target location in fixation coordinates
q
Displacement vector in fixation coordinates
Displacement vector in proprioceptive coordinates
Force (motor output)
Schematic of the computations involved in reaching
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1 1 2 1 2
1 1 2 1 2
1
2
1 2
1 2
1 1 2 1 2 2 1 2
1 1 2 1 2 2
cos( ) cos( )
sin( ) sin( )
sin( ) sin( ) sin( )
cos( ) cos( ) co
x
y
h
a t h
x x
y y
p l q l q q
p l q l q q
q
q
dp dp
dq dqdJ
dp dpd
dq dq
l q l q q l q qJ
l q l q q l
p
x s p
x x x
q
p
q
1 2
1
s( )
a
a
q q
d
d
d
d
J
pp q
q
px q
q
q x
p
1l
2l
s
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A
C
B0.5 sec
PPC cell
Control Task
Delay Task
Delay Task
D
F
E
0.5 sec
Somatosensory cortex cell
Control Task
Delay Task
Delay Task
PPC neurons encode target of intended movement during the delay period
Crammond and Kalaska 1989
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PPC neurons encode target of intended movement even after it disappears
Kalaska JF Can J Physiol Pharmacol 1996
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…left of fixation
Delayed pointingDelayed pointing with intervening saccade
Activation area when the remembered target is to the right of fixation
Human PPC neurons code for target location in fixation centered coordinates
Medendorp et al. 2003
Left cortex Right cortex
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Deltoid muscle
Primary motor
cortex cell
Posterior parietal cortex
cell (area 5)
Opposing load No load Assisting load
500 ms
10
0 im
p/s
PPC neurons encode target location and not the forces necessary to reach that target
Kalaska JF (1988)
Kal
aska
et a
l. J
Neu
rosc
i 198
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Experiment: rotate each eye by 180o. After 4-5 months, no sign of adaptation.
“When the piece of meat was moved back and forth in the water several centimeters above and a little to one side of the animals, they tilted their heads downward on that side and began to move toward the bottom of the aquarium. Even though the newts happened to be resting on the bottom when the lure was thus waved above them, they cocked their heads down under them and began pushing about among the pebbles of the bottom with the nose and forefeet. If the lure was placed below the animals, the head and forebody were tilted upward and the newts started toward the surface.”
Newts show an inability to adapt to radical changes in the optics of vision
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A
B
Day 3 Day 34
La
ten
cy (
s)
Pre- Days of reversing Post-
C
Primates adapt to radical changes in optics of vision
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xee
xtxdv
1
2
c1
c2
target
camera
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A B
Wedge prisms: rapid adaptation and equally rapid de-adaptation indicates short-term changes in existing networks
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With extensive training, throwing with wedge prisms can become a skill.
This indicates formation of a new
map for the prism and the ability to switch
on context.
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Model Copy
Patients with lesion in the right hemisphere may exhibit neglect of the left visual space
Marshall JC & Halligan PW (1995) Nature 373:521
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Committeri, G. et al. Brain 2007 130:431-441
Neglect of the extra-personal and personal space
Test for neglect of extra-personal space: Line bisection test, figure copying, reading a sentence.
Test for neglect of personal space: use a comb, use a razor to shave the face, use a lipstick.
Neglect of extra-personal space: lesion of the right frontal lobe, ventral premotor cortex
Neglect of personal space: lesion of the right inferior parietal cortex
STG: superior temporal gyrus
MFG: medial frontal gyrus
WM: white mater
SMG: supramarginal gyrus
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Prism glasses produce after affects that improves the sense of “straight ahead” in neglect patients
Rossetti Y. et al. (1998) Nature 395:166
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Prisms Controls
original
pre-
post-
late
Prism glasses produce after affects that reduce the neglect observed in PPC lesions
Rossetti Y. et al. (1998) Nature 395:166
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Apraxia
Apraxia is an inability to perform skilled movements, particularly tool use, in the absence of elementary motor deficits (weakness, normal posture or tone).
It is most commonly associated with damage to the parietal cortical areas of the left hemisphere.
When the patient is asked to demonstrate use of a screwdriver, the patient may position his hand as if holding a pen. When given a partially driven nail into a piece of wood, and a collection of tools, they may select a scissor to drive the nail rather than a hammer.
In performing a task that requires a sequence of actions, these patients may have difficulty in putting the acts in the proper order. For example, demonstrate how to prepare a letter and envelope for mailing.
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Understanding actions of others: the mirror neuron system
Social skills and theory of mind: the awareness that other people have beliefs and desires as we do, but different from our own, and that these beliefs and desires guides their actions. By observing their actions, we can guess their goals and intentions.
19 Fogassi et al. (2005) Science 308:662-667.
D
20 Fogassi et al. (2005) Science 308:662-667.
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Actions are planned in fixation centered coordinates:Position of the hand and the target are represented in terms of their
location with respect to the fixation.
Neurons combine proprioceptive information with visual information using a gain field.
Movements are planned in terms of goals, not in terms of detailed forces.
Lesion of the right parietal cortex can result in neglect. Lesion of the left parietal cortex can result in apraxia.
Mirror neurons might provide a mechanism through which we understand the intention of others.
Summary of the posterior parietal cortex
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