9/28 Cognitive control of movement (Burke)

Question 1

Describe the basic cellular organization of neocortex

Answer 1

1. Evolved later. 6 different layers, each with different cell types. I: molecular layer II: external granule layer III: extra pyramidal cell layer IV: Internal granule cell layer V: internal pyramidal layer VI: multiform layer All above white matter. Superficial layers (I-III), ascending, to layer IV. Deep layers (V,VI)

Question 2

Define the difference between neocortex and allocortex and give an example of each.

Answer 2

Allocortex has fewer than the six layers in neocortex. Two types: paleocortex (3-5 layers, parahippocampal gyrus, entorhinal cortex, piriform cortex, subcallosal area, cingulate gyrus. Archicortex (3 layers: molecular, pyramidal/granule, polymorphic) only in hippocampal formation—dentate gyrus, hippocampus proper. These are in limbic cortex.

Question 3

Define 3 major differences between primary motor (BA 4) and premotor cortex (BA 6)

Answer 3

BA6 is premotor and supplementary motor, BA4 is primary motor. BA6 results in coordinated movements. Direct pathways: BA6—to interneurons then higher in dorsal horn. BA4—to motor neurons then middle dorsal horn and ventral horn. Indirect: BA6—medial brain stem path, reticular spinal. BA4—lateral brain stem path, rubrospinal 3 differences: BA4 vs BA6—agranular vs transition from agranular to granular; single movement vs set related; different targets in the spinal cord.

Question 4

Define a ‘population code’ and describe why it is believed that this is the coding scheme of primary motor cortical neurons.

Answer 4

Represents stimuli using joint activities of a number of neurons. There are cells responsible for movement in each direction, but each cell is specific to a certain vector.

Question 5

Define the critical inputs one should consider when designing brain-machine interfaces for prosthetic limbs. In other words, what is one challenge that has kept prosthetic limbs from becoming common practice?

Answer 5

We did not consider sensory input when designing neuroprosthetics. Only looked at how activation of the motor cortex could move mechanical arms independent of physical movement

Question 6

Compare and contrast the different networks that support reach versus grasp.

Answer 6

Reaching—requires reciprocal connectivity between the intraparietal cortex and F1, F2, and F4. Grasping—requires F5 (ventral premotor cortex) AIP and more ventral posterior parietal cortex.

Question 7

Define canonical and mirror neurons, including where they are found and their activity properties.

Answer 7

Canonical=neurons in ventral premotor cortex that are activated during motor execution and in response to 3-D objects. i.e. monkey sees an object and they are activated throughout the initiation and completion of movement. Mirror neurons=neurons that act in the same way as canonical (fire during movement) but also fire when they witness the same action being accomplished by someone else. Thought to be the basis of learning (seeing and doing). Has to be an exact action, if the task is done in an unfamiliar way, there is no firing in the neurons used to complete the task themselves.

Question 8

Identify the different brain regions in which ‘mirror neuron’ activity patterns have been observed. BONUS: Can you design an experiment that would test an alternative hypothesis to the mirror neuron theory?

Answer 8

F5, ILP, LIP, M1, Pad, VIP, PM.
F5—mostly hands, one study found mouth and auditory. IPL also hand. LIP eye gaze. M1 (motor) reaching, tracking arm, and hand PTNs. PMd tracking arm. VIP bimodal tactile/visual. PM hand.

Question 9

Describe the experimental design and results that led researchers to conclude that rats have mirror neuron activity. Identify the brain region in which these cells were found.

Answer 9

Animal with silicon probe implant sits on a circular platform while witnessing the demonstrator receive high or low intensity shocks. Control: the shock is delivered in the grid next to the demonstrator and does not illicit pain. Laser condition: implanted animal is alone and a laser is shone in paws or tail, calibrated to pain intensity. CS condition: implanted animal alone and fear conditioned pure tone is played. Results: rat anterior cingulate cortex contains emotional mirror neurons that respond when a rat experiences pain and witnesses another rat in pain but not while experiencing another salient emotion, fear. Deactivation of the cingulate cortex caused reduced distress when witnessing another rat receive shock.