feedback control
task of loop is to minimize difference between desired input and actual output.
feedforward control
visual info (and memory) used to generate anticipatory command using internal model "memory" of the responses of muscles to neural commands - feedback control corrects for residual errors
does motor cortex control individual muscles or overall movement?
- evidence for control of single muscles
- firing of some motor cortex cells is well correlated with single muscle force
- focal stimulation via microelectrodes can activate muscles
- even TMS can activate single muscles if these are voluntarily pre-activated
motor cortex control for individual or overall movement?
-evidence for multiple muscles (synergies) and types of movement
- histology shows corticospinal tract axons nearly always innervate the motoneuronal pools of several muscles
- TMS ONLY actiavtes single muscle that are voluntarily pre-activated. increase TMS strength recurits lless pre-activated muscles
- spike -triggered averaging of EMG: response in more than one muscle.
4 muscles dhowed EMG response following spikes in single motor cortex neuron.
motor cortex neurons organized?
output neurons cause ? and respond to
deeper into cortex = more or less firing?
in columns of input/output modules
cause movement & respond to movement-related sensory feedback .
less firing as it goes deeper in ocrtex.
cortical popln vectors
- preferred ??
- what is population vector?
- centre-out movement indicates?
direction
vectorial sum of all individual neurons’ preferred direction vvectors.
indicates group activity of cortical neurons is well correlated w movement direction.
effect of loading arm on cortical neuron’s firing rate as monkey performs movements in different directions.
polygon arouns area showing firing rates increases in sie the more the load direction opposes the preferred direction.
conclusions
voluntary movement direction predictable from poln vector
- firing rates of MC neuron depend on external load
- firing rate depend on precision, speed, relevance and importance of movement, not just direction and force
- some MC neurons only fire if individual joint involved
- MC nuerons sometimes not directly connected to spinal MNS
few functions of supplementary and premotor areas
- upstream from MC
- inputs from motivational aras.
- generate commands for movement
match posture to voluntary
coordinate L&R hands.
visuomotor coordination
- visual perception different than visual-guided acts.
ventral stream mediates?
dorsal stream mediates?
V - what = shape recognition and discrimination
D - where/how = motor responses
MC lesions
hemiplegia loss of fine finger and hand movement spasticity babinski response (normally curl toe, babinski = fan toe dysarthria
SMA, premotor lesions
apraxia
poor bilateral coordination
