L40. Modulation of Movement Flashcards
What is the role of the motor cortex?
- Initiation of voluntary movement
- Skilled, dextrous movements
- Integration of movement
- Maintenance of postural stability goals
- Response to the physical environment
How is the topography of the periphery generally mapped in the motor cortex?
The motor homunculus
- Lower limbs towards the midline of the motor cortex
- The Upper limbs more superiolaterally
- The face is lateral
Describe what arteries supply the primary motor cortical regions?
The anterior cerebral artery supplies the medial side of the motor cortex (lower limbs) and the rest of the cortex is supplied by the middle cerebral artery
Is there only the one clear set motor homunculus map in the primary motor gyrus?
No.
The motor homunculus is not a clearly distinguishable topography with definite set areas.
There is also probably more than one motor homunculus-like mapping organisation especially within the association areas of the cortex.
The motor homunculus map isn’t the best representation of the primary motor cortex because neurons devoted to one particular part of the body cannot be mapped directly to one specific area of the cortex alone.
Describe a topographic map of movement in the primary cortex that is more appropriate
There are territories devoted to different regions of the body and a distinciton between areas that…
- project directly in the corticospinal tract
- respresent complex patterns in the corticobulbar tract
If a person is asked to perform a simple movement involving a small subset of related muscles… what areas of the brain do you think would be primarily involved?
- Areas of the primary motor cortex involved in innervating that group of muscles
- The somatosensory cortex region that is involved with sensation of that area as a direct consquence of that muscle movement
If a person is then asked to perform a complex movement with a temporal pattern involved what areas of the brain do you think would be primarily involved?
- Areas of the primary motor cortex involved in innervating that group of muscles
- The somatosensory cortex region that is involved with sensation of that area as a direct consquence of that muscle movement
- Recruitment of the motor association area of the anterior cortex due to an ongoing temporal change in movement
If a person is then asked only to think about performing the complex movement with a temporal pattern involved what areas of the brain do you think would be primarily involved?
- Only the motor association would be involved as where the intetntions are put together before signalling the motor cortex to act
Experiment: Continual stimulation of a single area of the monkey’s brain. It lead to the monkey bringing the hand to the face from no matter where the hand was before stimulation.
What inferences can be made about representation in the motor cortex?
It suggests that there is a GOAL DIRECTED organisation of the cortex and motor neurons don’t represent muscles or movement but the end point of a sequence of a movements
Because despite stimulating the same area of the brain:
- There is innervation of different muscles each time
- There is different directions and forces each time
What is another source of evidence to show that the neurons of the motor cortex encode end points and not muscle groups
Measuring the firing rate of a neuron when a person is performing a precision group vs. power grip
- The precision grip - the neuron was highly active in the movement
- The power grip - The same neuron was not involved at all (despite using the exact same muscle groups only adding power)
What is meant by mirror motor neuron activity?
- Performing a task activates a specific set of motor neurons in the cortex
- Simply watching the same task being performed by another person elicis the same motor neurons to be activated.
Are these visually guided motor neurons related to hand actions or the goal?
They are related to the specific hand movements (watching a similar movement but with a different end point elicited the same response). It only fires to the sequence of muscle activity
What about if you are blind folded and produce that same movement, do the visual/mirror motor neurons firs?
Yes they do
The motor units respond by the movement
What is the main significance of these visual/mirror motor neurons
It is believed that this is a major mechanism by which we learn skilled tasks and movements.
We learn a lot by watching other people and copying them.
The brain is recognised to “know” what is happening in other peoples brains when they are performing tasks
What information does the motor cortex require in order to make movements?
- Requires input from sensory systems
- Requires pre-frontal and higher order systems to make a meaningful and decision oriented movements