Primary Motor cortex & somatosensory cortex

What is the primary motor cortex (M1)? Layers?

Located front of the central sulcus, is the area that provides the most important signal for the production of skilled movements
- has layer 5 neurons (Betz cells) that are the largest and send AP down descending spinal tract
- layers 1 to 4 is where planning occurs

What is the motor homunculus?

Topographic representation of the body parts and its correspondents along the precentral gyrus of the frontal lobe
- scientific accuracy impossible
- tries to show us what body parts are affected most
- stimulation in certain parts of brain causes certain movements

How does M1 activate?

Example of flexion and extension of wrist movements
- movement is pre-planned and M1 fires before it occurs
- when movement is being done, firing rates stop

What is M1 population vector?

M1 fires mostly when it moves in a particular/preferred direction & is silent in the other

Different neurons within M1 population will have different preferred directions of movements (this is where they are most active)

At each angle, there are multiple M1 neurons (each line is one)
- length of line = firing rate (long = more)
- red arrows represent population vector (average for various movements tested)
- each blob is same neurons as other blobs

M1 population vector spiraling?

No matter direction of spiraling, population vector spirals before movement vector
- pop vector predicts movement vector
- for outside to in, spirals are below line
- for in to outside, spirals are above line

Population vector vs movement vector?

Population vector:
- sum of the preferred directions of a population of neurons, weighted by the respective spike counts

Applications of M1 po[ulation vector?

Can be applied new technologies for disabled or not able-bodied people
- use brain to think of movement and tech can perform the movement

What is the somatosensory cortex? Parts?

Responsible for processing somatic sensations
- located behind frontal sulcus on postcentral gyrus (outwards)

VPLn:
- ventral posterior lateral nucleus relays somatosensory info from body

VPMn:
- ventral posterior medial nucleus relays somatosensory info from face/oral cavity

Where does info come from for somatosensory cortex?

Represented by homunculus
- lots of info from face and hands (sensitive areas) - also genitals

What is phantom limb? Map?

Condition in which patients experience sensations, whether painful or otherwise, in a limb that does not exist
- after losing body part, brain will use that space for another body part's info
(braille people, one finger has a bigger space, takes more info than other fingers)

Map is plastic and subject to change depending on use