Transcript Document

JHU BME 580.422 Biological Systems II
Adaptation of Visuomotor Maps
Disorders of parietal cortex
Reza Shadmehr
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Schematic of the computations involved
in reaching
hand location in
fixation coordinates
Displacement vector
in fixation
coordinates
Force (motor output)
q
xh
xa
q
Dq
q
xt
Proprioceptive
state of the body:
arm, head, and
eye positions
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Target location in
fixation coordinates
Displacement vector
in proprioceptive
coordinates
f
 p x  l1 cos( q1 )  l2 cos( q1  q2 ) 
p 

 p y   l1 sin( q1 )  l2 sin( q1  q2 ) 
xh  s  p
x a  xt  x h
q 
q   1
 q2 
 dp x dp x 


dp  dq1 dq2 
J

dq  dp y dp y 


 dq1 dq2 
 l1 sin( q1 )  l2 sin( q1  q2 ) l2 sin( q1  q2 ) 
J 

 l1 cos( q1 )  l2 cos( q1  q2 ) l2 cos( q1  q2 ) 
dp
Dp 
Dq
dq
dp
xa 
Dq
dq
Dq  J 1x a
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p
l2
s
l1
PPC neurons encode target of intended movement during
the delay period
PPC cell
A
Somatosensory cortex cell
Control Task
D
Control Task
0.5 sec
0.5 sec
B
Delay Task
E
Delay Task
C
Delay Task
F
Delay Task
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Crammond and Kalaska 1989
PPC neurons encode target of intended movement even
after it disappears
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Kalaska JF Can J Physiol Pharmacol 1996
Human PPC neurons code for target location in fixation
centered coordinates
Delayed pointing
Delayed pointing with
intervening saccade
Left cortex
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Activation area when
the remembered target
is to the right of
fixation
Right cortex
…left of fixation
Medendorp et al.
2003
PPC neurons encode target location and not the forces
necessary to reach that target
Opposing load
No load
Assisting load
Kalaska et al. J Neurosci 1989
Deltoid muscle
Primary
motor
cortex cell
Posterior
parietal cortex
cell (area 5)
100 imp/s
500 ms
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Kalaska JF (1988)
Newts show an inability to adapt to radical changes in the
optics of vision
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.”
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Primates adapt to radical changes in optics of vision
Latency (s)
A
Pre-
Days of reversing Post-
B
C
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Day 3
Day 34
camera
target
xdv
xt
xee
q1
c2
c1
10
q2
Wedge prisms: rapid adaptation and equally rapid deadaptation indicates short-term changes in existing networks
A
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B
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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Patients with lesion in the right hemisphere may exhibit
neglect of the left visual space
Model
Copy
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Marshall JC & Halligan PW (1995) Nature 373:521
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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Committeri, G. et al. Brain 2007 130:431-441
Prism glasses produce after affects that improves the sense
of “straight ahead” in neglect patients
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Rossetti Y. et al. (1998) Nature 395:166
Prism glasses produce after affects that reduce the neglect
observed in PPC lesions
Prisms
Controls
original
prepostlate
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Rossetti Y. et al. (1998) Nature 395:166
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.
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D
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Fogassi et al. (2005) Science 308:662-667.
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Fogassi et al. (2005) Science 308:662-667.
Summary of the posterior parietal cortex
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.
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