Higher Motor Control
2nd ed: Ch 5: cerebellum (152), basal ganglia
(157), supplementary motor area (162),
parietal lobes (167).
Apraxia: Gazzaniga et al, Cognitive
Neuroscience, pp. 401-404.
Major Brain Regions
Cortical:
A. Primary motor cortex
B. Secondary motor cortex
(supplementary motor area + pre-motor cortex)
C. Left parietal lobe
Subcortical:
D. Basal Ganglia
E. Cerebellum
Cortical Motor Regions
A. Primary Motor Cortex
• Provides primary motor signal from
cortex
• Selects which muscle groups to move,
and how forcefully
• Damage: weakness or paralysis in
corresponding region, imprecision of
fine motor movements
A. Primary Motor Cortex
Mrs. AL: AL suffered a stroke which affected the left Primary Motor Cortex in
the region corresponding to the right hand. "At first, I couldn't use the hand at
all, it was as if it was paralysed. Then slowly, I started to get it to move. Now, I
can use it to do some simple things, like helping me put on my hat, but I don't
seem to have any strength in it, and I can't do anything very sophisticated. I
dropped my wallet so many times trying to open it that I now use a pouch on
string which I carry around my neck. But the hardest part was learning to write
with my left hand. I still can't write anything at all with the bad hand. With the
left, I now write simple shopping lists and sign my name but my writing looks
babyish and clumsy".
B. Secondary Motor Cortex
= Supplementary Motor Area + Pre-Motor Cortex
Supplementary motor area
Pre-motor cortex
• Involved in generating plans for complex activities
e.g. novel movements, movement sequences
• Also involved in “control” - selecting amongst competing
motor plans
B. Secondary Motor Cortex
Damage:
1. can't perform complex tasks (sequencing errors)
• e.g. placing match to candle before lighting it
2. difficulties with bimanual coordination:
B. Secondary Motor Cortex
Damage (cont.):
• 3.
externally-driven movement
selection:
As part of a case presentation to staff at a rehab hospital, Mrs. J
was interviewed by the charming and handsome neurologist Dr.
C. During the interview, her right hand would repeatedly come
to rest on Dr. C.'s left knee, much to her own amusement and
that of the staff. She insisted that she had no control over this
gesture - that it was like her hand had "a mind of its own!"
C. Left Parietal Lobe
• Storage/retrieval of commonly-used complex action programs
e.g. turning key in a lock
• Also needed for planning novel sequences, esp. those
comprising familiar movements
C. Left Parietal Lobe
Damage = apraxia (or "limb apraxia"):
• inability to perform familiar, well-learned routines
• object use errors
• also problems with novel movements
A patient with bilateral lesions of the parietal lobes was unable to continue her
work as a fish filleter. When attempting to perform a routine that she had
completed thousands of times, she correctly inserted the knife point into the head
of the fish, began the first stroke, but then stopped. She claimed to know how the
action should be completed but could not execute it. At home, she found herself
putting the sugar bowl in the refrigerator or the coffee pot in the oven.
C. Left Parietal Lobe
Object use errors: most clearly seen when P must perform on
command and/or without object as prompt
e.g. Body-part error:
C. Left Parietal Lobe
May also make errors in novel sequences (e.g. perseverations)
C. Left Parietal Lobe
• Left parietal lobe and
Secondary motor cortex damage produces some
similar features
-> both regions may work
together to retrieve and
execute complex routines
D. Basal Ganglia
• Loop-like connections to motor cortex; regulates
activity in motor cortex
• Ensures that only the most highly activated motor
plan/signal is executed
• Rich in dopaminergic neurons
D. Basal Ganglia
• Important when a new movement plan is required:
- commencing a new motor activity
- ceasing a current motor activity
• Also involved in setting posture
D. Basal Ganglia
Parkinson’s disease
• depletion of dopaminergic neurons in BG - motor signals
from cortex are overinhibited
• difficulty initiating movement (“hypokinesia”)
• movements are slowed (“bradykinesia”)
• external cues may help to overcome:
"First the feet freeze and feel as if they are glued to the ground. When you
eventually get going, the top half of the body seems to go faster than the bottom
and you end up running and sometimes the only way to stop is to run into
something. This can often lead to bumps and bruises. Some patients often find it
easier to go up and down stairs or to step over objects. It often helps to imagine
there is something on the ground in front of you and you have to step over it."
D. Basal Ganglia
Huntington’s Chorea:
• Atrophy of Basal Ganglia
• Reduced output from BG means reduced inhibitory control
over motor signals from cortex
• Involuntary movements (”chorea”)
E. Cerebellum
• Loop-like connections to other motor areas; also receives
somatosensory info.
• Fine-tuning and timing of movements
-> Esp: fast, precise actions (ballistic movts), actions
requiring continuous feedback
• Damage:
- "drunken" gait
- slurred speech
- action tremor, esp. when reaching (ataxia)
- ballistic movt errors (overshooting target)
- time judgements
Functional Map of Motor Regions
Left Parietal
Lobe
Secondary
Motor Cortex
Cerebellum
Primary Motor
Cortex
Brainstem
Spinal Cord
Basal
Ganglia