3 principles of sensorimotor function
- hierarchically organized; parallel structure, functional segregation
- motor output guided by sensory input - need sensory (proprioception/somatosensory) to know how to adject motor output.
allow for flexibility in changing enviro. - learning can change the nature and locus of sensorimotor control first learning = high brain areas. well learned = lower brain areas.
ballistic movements
all-or-none. dont need sensory feedback. re-do whole action if it went wrong.
2 major areas in movement initiation
PPC
Dorsolateral Prefrontal cortex (DL PFC)
PPC - job, modality, output? stimulation
- directs attentino and creates intention to perform action
mutli-modal - takes in various sensory iputs.
output to motor cortex, DLPFC, M2, frontal eye field (attention directed eye movement)
low stimulation - patient had intention to perform action
high stimulation = patient thought they had performed action
damage to PPC
sensorimotor deficits
- reaching, grasping, attention
apraxia
disorder of voluntary movement
- cant make specific movements when requested to do so, especially imaginary, when out of context.
bilateral damage = bilateral symptoms. unilateral damage = contralateral effect/symptom
contralateral neglect
inability to respond to stimuli on apposite side of damage
often right PPC damage = left side of world doesnt exist. probrlme of conscious attending
dorsolateral PFC - fxn, input, projects to?
evaluates external stimuli - knows internal goals, ensure external and internal goals align.
activity depends on object characteristics and/or location of object.
can either “ok” or put brakes on PPC initiation of movement.
projects to m2, m1, frotnal eye field and PPC.
M2 - input, output, important areas? stimulation? fxn?
input from PPC and DLPFC
output to M1.
supplementary motor area and pre-motor cortex.
stimulation = complex movements - directed program. neurons active before and throughout movement.
involved in programming specific movement patterns
mirror neurons
fire when performing movement and when watching other do same movement.
= learn task from watching.
care about reaching for goal object not non-goal object.
possibly important for social cognition. social understanding, imitation, cooperation. - fire to action, regardless how it is detected.
where are mirror neurons? in humans?
PPC - respond to purpose of action. if action relevant like eating.
not confirmed in humans. - little evidence for it.
but, EMG showed residual motor activation after watching but never moving.
M1 - where? what? conventional vs current view of organization
precentral gyrus. point of convergence & departure of sensorimotor signals.
conventional: motor homunulus - hand and mouth more area. basically mirror of sensory homunculus.
current view: stimulating = complex motor outputs ex: feeding response. revealed crude somatotopic organization. areas of brain are organized more in way of complex actions. different areas of body close together to elicit complex movement.
PMC neuron and direction
- penfield said each neuron has preferred direction. fire before and during movements of preferred direction
- conventional: neurons fire more when closer to goal.direction doesnt matter
sensorimotor system is inherently plastic. location in M1 produces?
each location in M1 can produce innumerable patterns of muscle contraction from start to target location.
action map in addition to homunculus.
plastic with seensorimotor feedback.
PMC lesions
mild effects. large lesions may disrupt movement of body parts indepently of others.
doesnt eliminate voluntary movement. M1 can be skipped. and easy to correct inappropraite movements
