1. Chapter 8 Control of Movement

2. The Cerebral Cortex
The primary motor cortex is located in the precentral gyrus located in the frontal lobe
The motor cortex does not send messages directly to the muscles.
Axons from the precentral gyrus connect to the brainstem and the spinal cord, which generate impulses that control the muscles

3. See the video: https://www.youtube.com/watch?v=ogBX18maUiM&t=83s

5. The Cerebral Cortex (cont’d.)
Specific areas of the primary motor cortex are responsible for control of specific areas of the opposite side of the body
Some overlap does exist
The primary motor cortex is active when people intend a movement
The primary motor cortex “orders” an outcome

8. Units of Movement (cont’d.)
Other areas near the primary motor cortex also contribute to movement
Posterior parietal cortex: keeps track of the position of the body relative to the world
Damage to this area have trouble finding objects in space, even after describing their appearance accurately.
When walking, they frequently bump into obstacles
Important for planning movement

9. Units of Movement (cont’d.)
Cells in the following areas are involved in the preparation and instigation of movement
Prefrontal cortex
Responds to lights, noises, and other sensory signals that lead to movement
Calculates predictable outcomes of actions and plans movement according to those outcomes

10. Prefrontal cortex
If you had damage to this area, many of your movements would be illogical or disorganized, such as showering with your clothes on or pouring water on the tube of toothpaste instead of the toothbrush
Interestingly, this area is inactive during dreams, and the actions we dream about doing are often as illogical as those of people with prefrontal cortex damage
If you do something absent-minded first thing in the morning, it may be that your prefrontal cortex is not fully awake.

11. Units of Movement Premotor cortex
Active during preparation for movement
Receives information about a target
Integrates information about position and posture of the body; organizes the direction of the movement in space
Supplementary motor cortex
Organizes rapid sequence of movements in a specific order; inhibitory if necessary
If you have a habitual action, such as turning left when you get to a certain corner, the supplementary motor cortex is essential for inhibiting that habit when you need to do something else

12. Units of Movement (cont’d.)
Mirror neurons are neurons that are active during both preparation of a movement and while watching someone else perform the same or similar movement
May be important for understanding, identifying, and imitating other people
May be involved in social behaviors
Unknown whether they cause or result from social behavior
See the videos:

14. Implications of Mirror Neurons for Real Life

15. Units of Movement (cont’d.)
The conscious decision to move, and the movement itself, occurs at two different times
A readiness potential is a particular type of activity in the motor cortex that occurs before any type of voluntary movement
Begins at least 500 ms before the movement itself
Implies that we become conscious of the decision to move after the process has already begun

17. The Cerebellum
The cerebellum is a structure in the brain often associated with balance and coordination
More neurons in the cerebellum than in all other brain areas combined
Damage to the cerebellum causes trouble with rapid movements requiring aim/timing
Examples: clapping hands, speaking, writing, etc.
See a video here:

18. The Cerebellum
People with cerebellar damage are normal, however, at a continuous motor activity.
For example, they can draw continuous circles, like the ones shown here.
See a video of finger-to-nose test for diagnosis:

19. The Cerebellum
Cerebellum is one of the first brain areas that alcohol affects.
The symptoms of cerebellar damage resemble those of alcohol intoxication: clumsiness (awkward in movement ), slurred speech, and inaccurate eye movements.

20. The Cerebellum (cont’d.)
Studies suggest that the cerebellum is important for the establishment of new motor programs that allow the execution of a sequence of actions as a whole
Important for tasks that require timing
The cerebellum also seems critical for certain aspects of attention, such as the ability to shift attention and attend to visual stimuli

21. The Cerebellum (cont’d.)
The cerebellum receives input from the spinal cord, from each of the sensory systems and the cerebral cortex, and sends it to the cerebellar cortex
The cerebellar cortex is the surface of the cerebellum

22. Brain Areas and Motor Learning
The learning of new skills requires multiple brain areas involved in the control of movement
Basal ganglia is critical for learning motor skills, organizing sequences of movement, “automatic” behaviors, and new habits
Example: driving a car
Relevant neurons in the motor cortex also increase their firing rate; the pattern of activity becomes more consistent as the skill is learned

23. Inhibition of Movements
Antisaccade task: inhibit a saccade, a voluntary eye movement from one target to another
Performing this task well requires sustained activity in parts of the prefrontal cortex and basal ganglia before seeing the moving stimulus
Ability to perform this task matures through adolescence

24. Movement Disorders
Parkinson’s disease is a movement disorder characterized by muscle tremors, rigidity, slow movements, and difficulty initiating physical and mental activity
Associated with an impairment in initiating spontaneous movement in the absence of stimuli to guide the action
Symptoms also include depression, memory and reasoning deficits, loss of olfaction, and other cognitive deficits

25. Parkinson’s Disease (cont’d.)
Caused by gradual and progressive death of neurons, especially in the substantia nigra
Substantia nigra sends dopamine-releasing axons to the caudate nucleus and putamen
Loss of dopamine leads to less stimulation of the motor cortex and slower onset of movements

27. Parkinson’s Disease (cont’d.)
Studies suggest early-onset Parkinson’s has a genetic link
Genetic factors are only a small factor of late onset Parkinson’s disease (after 50)

28. Parkinson’s Disease (cont’d.)
Exposure to toxins are one environmental influence
MPTP found in some illegal drugs and pesticides
MPTP is converted to MPP+, which accumulates and destroys neurons that release dopamine

31. Parkinson’s Disease (cont’d.)
Cigarette smoking and coffee drinking are related to a decreased chance of developing Parkinson’s disease
Damaged mitochondria of cells seems to be common to most factors that increase the risk of Parkinson’s disease

32. Parkinson’s Disease (cont’d.)
The drug L-dopa is the primary treatment for Parkinson’s and is a precursor to dopamine that easily crosses the blood-brain barrier
Often ineffective and especially for those in the late stages of the disease
Does not prevent the continued loss of neurons
Enters other brain cells, producing unpleasant side effects

33. Parkinson’s Disease (cont’d.)
Other possible treatments for Parkinson’s:
Antioxidant drugs
Drugs that stimulate dopamine receptors
Neurotrophins (proteins that induce survival of neurons) to promote neuron survival
Drugs that decrease apoptosis (programmed cell death)
High frequency electrical stimulation of the globus pallidus (Globus pallidus is constantly inhibiting the thalamus. Thalamus retransmit sensory and motor signals to the cerebral cortex)

34. Parkinson’s Disease (cont’d.)
Implantation of neurons from aborted fetuses remains controversial and only partially effective
Only moderate benefits seen
Stem cells are immature cells grown in tissue culture that are capable of differentiation
Are an attractive alternative

35. Huntington’s Disease
Huntington’s disease is a neurological disorder characterized by various motors symptoms
Affects 1 in 10,000 in the United States
Usually onset occurs between age 30-50
Associated with gradual and extensive brain damage especially in the caudate nucleus, putamen, globus pallidus, and the cerebral cortex
See a video here:

37. Huntington’s Disease (cont’d.)
Initial motor symptoms include arm jerks (involuntary muscle movements) and facial twitches
Motors symptoms progress to tremors and writhing (twisting body) that affect the persons walking, speech, and other voluntary movements
Also associated with various psychological disorders:
Depression, memory impairment, anxiety, hallucinations/delusions, poor judgment, alcoholism, drug abuse, sexual disorders

38. Huntington’s Disease (cont’d.)
Presymptomatic tests can identify with high accuracy who will develop the disease
Controlled by an autosomal dominant gene on chromosome #4
The higher the number of consecutive repeats of the combination C-A-G, the more certain and earlier the person is to develop the disease

40. Huntington’s Disease (cont’d.)
A variety of neurological diseases are related to C-A-G repeats in genes
For a variety of disorders, the earlier the onset, the greater the probability of a strong genetic influence
Identification of the gene for Huntington’s disease led to the discovery of the protein that codes it (huntingtin)
Mutant form impairs neurons in the brain and future drug therapy may address huntingtin