Motor Control - McCausland Center

ugliestmysticAI and Robotics

Nov 14, 2013 (3 years and 10 months ago)

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1

Motor Control


Chris Rorden


Ataxia


Apraxia


Motor Neurons


Coordination and Timing


2


M1

Primary Motor Strip


M1

sends outputs to muscles


Motor strip most posterior portion
of frontal cortex


Topic of future lecture


Damage to M1 leads to
paresis (weakness, partial
loss of movement, impaired
movement) or plegia
(complete paralysis). For
example, after stroke many
patients have hemiparesis
(poor use of contralesional
limbs).

3

Cortical visual processing

M
-
ganglion cells

P
-
ganglion cells

Magno

LGN

Parvo

LGN

V1

V1

V2

V2

V3

V4

MT

V5

IT

cortex

Parietal

Dorsal system is fast, but color blind.

Helps with motor control (Where/How).

Ventral system is slow, but detailed.

Helps with object identification (What).

4

Where versus What


Dorsal damage: action


Akinetopsia: Motion Blind


Spatial perception problems


Problems with reaching, eye movements


Ventral damage: recognition


Achromatopsia: Colorblind


Agnosia: object identification


5

Visual Form Agnosia


DF has ventral damage


Profound agnosia :: can not even tell orientation of object


Motor control accurate :: motor system functions
accurately.

Patient DF

Controls

Posting task

Perceptual

matching

Posting

6

Ventral vs Dorsal damage
(Goodale et al. [1994]
Curr Biol. 4:604
-
610)

When shown two
shapes (left),
DF

was
poor at saying if the
shapes were same or
different,
RV

was
good at this task.

DF

RV

chance

100%

0%

DF

Control

RV

Frequency

25%

0%

Distance from centre (mm)

0 15

0 15

0 15 30

When asked to grasp an
object,
DF

grasped near
the centre (like healthy
people),
RV

was poor
at this task.

7

Ataxia


Ataxia (from Greek ataxiā, meaning failure to
put in order) is unsteady and clumsy motion of
the limbs, with poorly coordinated movements.


Optic ataxia results from a lesion in the
superior parietal lobe, which can be bilateral; it
causes an impairment in the automatic visuo
-
motor transformation (either or both in reaching
and/or grasping visual targets) in actions with
the hand contralateral to the lesion site;

8

Perception and action dissociate


In spite of visuomotor impairment, optic ataxic
patient AT can recognize shape and size of
visual objects (Jeannerod, Decety, Michel,
1994).


AT cannot reach and/or grasp object with
precision grip, but she can
estimate

size of
object by scaling the distance between thumb
and index.


Unlike DF, AT’s performance in task of
pointing

(index) is improved if
delayed

by 5 seconds
between occurrence of stimulus and launching
of action.

9


Maximum grip aperture
seen at 60% of
movement to target.


After lesion of superior
parietal lobe, optic
ataxic patients are
impaired (bilaterally) in
(B) grasping with
precision grip and in
(C) reaching

10

Apraxia


Apraxia (Greek without action or working): loss
of the ability to execute or carry out learned
purposeful movements, despite having the
desire and the physical ability to perform the
movements.


Apraxic patients are unable to use and
recognize tools, to pantomime the use of
imaginary tools and to understand others’
pantomimed actions using imaginary tools; but
their visuo
-
motor transformation is intact.


11


Most argue apraxia results from a lesion
in the left inferior parietal lobe


A careful study by Goldenberg shows
pantomime specific to left insula.

12

Perception versus Action


Haffenden, Schiff&
Goodale (2001)


Titchener illusion is
perceptually powerful


However, grasping
shows reduced bias.


13

Perception versus action


Bridgeman (1975) et & Goodale et al. (1986)
find that healthy subjects can point accurately
index finger towards target even though they
are not visually aware of target motion because
it coincided with saccadic eye movement.


Castiello et al. (1991) find that healthy subjects
can correct online trajectory of their hand
movement towards moving target 300 ms
before they are visually aware of target’s
change of location.


Visual awareness of object subsequent to, and
not necessary for, accurate visual control of
action on object (cf. DF).

14

Coordination and Timing


Movement coordination requires timing.


In particular, bimanual movements.


Amazingly, split brain patients show
precisely timed movements when moving
both hands.


Many believe cerebellum plays key role
in sequencing and timing.