Motor Cortex Flashcards
MI
Primary motor cortex
SMA
supplementary motor area
PMd
dorsal premotor cortex
PMv
ventral premotor cortex
FEF
Frontal eye fields
SEF
supplementary eye field
Where is SMA
The supplementary motor area is dorsally located and anterior to the MI
Where is the PMv
the ventral premotor cortex is anterior and ventralish to the motor cortex
PEF
parietal eye fields
APA
Arcuate premotor area
What is the APA responsible for
Arcuate premotor area is involved in hand and arm fields
Explain the frontal motor loop
The frontal motor areas are linked by loop pathways to posterior cortical areas, the basal ganglia & the cerebellum. They ultimately link back to themselves, hence the loop. Another part of the loop includes the frontal and parietal eye fields.
What is the result of lesions to the MI
Lesions on the primary motor cortex result in inability to use the muscles associated with the lesioned space. This includes strength. It’s not total. There can be some movement and strength but its limited and maybe in this case study it was just because some areas were left in tact?
Somatotopy of MI
medial and interior bottom to top: toes, ankle
medial dorsal to ventral lateral: knee, hip, trunk, shoulder, elbow, wrist, hand, little finger, ring finger, middle finger, index finger, thumb, neck, brow, eyelid and eyeball, face, lips, jaw, tongue, swallowing (last three areas include salivation) (Last five areas include vocalization)
How do neurons in MI relate to muscle movement?
EMG activity in monkeys reveals that muscle movement triggers action potentials in MI. One neuron’s activity can be correlated with multiple muscles.
Explain the Georgopoulos et al. experiment on population vectors in MI and their importantce
Monkeys made arm movements to various directions and singe neurons were measured.
Many of the neurons responded most strongly to specific directions of movement and gradually responded less strongly as the direction of movement went away from the preferred direction. This was represented in a Tuning curve. There was overlap on the curve. This overlap also shows that motor neurons did not have one direction and would respond to other directions as well. They worked in conjunction with other neurons to generate a directional movement.
The motions they were active for were mostly directed. Less directed contractions of the same muscles did not show activation.
Doesn’t answer whether it’s about muscle or movement selectivity
Population vector
In neuroscience, a population vector is the sum of the preferred directions of a population of neurons, weighted by the respective spike counts.
How does a population vector related to directional movement?
If you have a four neurons whose preferred direction is 90 degrees apart, like a cross, and two of them next to each other are firing, then the direction of movement will average the difference at the 45 degree direction.
One big question repeated in the lector on motor cortex?
Is it about muscle selectivity or movement selectivity?
What study answered the question about muscle or movement selectivity and what did it reveal?
Kakei, Hoffman & Strick had a monkey move a lever with just a wrist movement. They turned the wrist so that in one part of the task the palm was down (pro/prone) and the other part the palm was up (sup/supine). They also had a middle version with the palm facing in. The monkey flexed (curled the wrist) or extended (pulled back on the wrist) to move a lever. The neurons fired according to the direction of the hand, not according to whether it was flexing. So if it fired while flexing when the hand was pro, it fired while extending when the hand was sup.
This can also be phrased as encoding extrinsic direction of the motion (right, up, left, down) rather than anatomical direction (extension, flexion, ulnar, radial).
CM cells
Corticomotoneuronal cells in the caudal (posterior) portion of M1 (recently developed). M1 (primary motor cortex). They are output neurons that synapse with mononeurons in the spinal cord.
They can be active in movements toward multiple directions. They are “functionally tuned” and mediate the muscle’s contribution only to a subset of movements in which it participates. For example, acceleration in a muscles preferred direction and braking the opposite direction.
In other words, the preferred direction of the corticomotoneuronal cell may not be the same as the muscles preferred direction. Also, they may be selectively active for different muscle tasks, such as stabilizing or generating force.
Somatopic mapping in the human SMA
SMA (Supplementary Motor Area) has complex mapping that isn’t as neat as in M1. It’s complicated and was tested through electrical stimulation.
SMA lesions
Supplementary Motor Area lesions have a subtle effect. It is large at first, but then improves. The deficits include bimanual coordination (doing different things with different hands at the same time). AKA. clench one hand while spreading the other.. Also, serial gestures like moving the thumb to each finger of the hand.
SMA neural recording for bimanual coordination.
One neuron active for movement of only the right hand, another for only left hand, and a third for both hands together were discovered. They were active before and during movement.
