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
Dorsal system is fast, but color blind.
Helps with motor control (Where/How).
Parietal
MT
V5
M-ganglion cells
Magno
LGN
P-ganglion cells
Parvo
LGN
V1
V1
V2
V3
V2
V4
Ventral system is slow, but detailed.
Helps with object identification (What).
IT
cortex
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
Posting task
Perceptual
matching
Posting
Controls
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.
chance
0%
DF RV
Control
25%
DF
RV
Frequency
When asked to grasp an
object, DF grasped near
the centre (like healthy
people), RV was poor
at this task.
100%
0%
0
15 0
15 0
15
30
Distance from centre (mm)
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 visuomotor 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.