Higher Motor Control

1. 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.

2. Major Brain Regions Cortical: Primary motor cortex Secondary motor cortex (supplementary motor area + pre-motor cortex) Left parietal lobe Subcortical: Basal Ganglia Cerebellum

3. Cortical Motor Regions

4. 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

5. 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".

6. B. Secondary 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 Supplementary motor area Pre-motor cortex

7. B. Secondary Motor Cortex Damage: • can't perform complex tasks (sequencing errors) • e.g. placing match to candle before lighting it • difficulties with bimanual coordination:

8. B. Secondary Motor Cortex • 3. externally-driven movement selection: Damage (cont.): 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!"

9. 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

10. C. Left Parietal Lobe 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. • Damage = apraxia (or "limb apraxia"): • inability to perform familiar, well-learned routines • object use errors • also problems with novel movements

11. 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:

12. C. Left Parietal Lobe May also make errors in novel sequences (e.g. perseverations)

13. 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

14. 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

15. 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

16. 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."

17. 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”)

18. 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

19. Functional Map of Motor Regions Left Parietal Lobe Secondary Motor Cortex Basal Ganglia Cerebellum Primary Motor Cortex Brainstem Spinal Cord