NROC64H3 Lecture Notes - Deeper And Deeper, Semicircular Canals, Motor Control

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Published on 19 Apr 2013
School
UTSC
Department
Neuroscience
Course
NROC64H3
Professor
Chapter 9 Motor Systems
Why Studying Motor System is Difficult
- To stimulate it have to know what is appropriate pattern of stimulation to apply in order to get
a response
o 2nd - Sensory system is largely straightforward way from level to level but a
characteristic of motor control is that every action necessarily results in sensory
feedback (from muscle, join and vision and other special senses)
- Better approach apply real stimuli to the senses & trace the resultant pattern as they
penetrate deeper & deeper through levels of NS & emerge at motor end as movements
o Not possible w complex system ( e.g. movement of hand) but w number of levels is
much smaller ( i.e. primate brain of insects or in simpler sub-system of mammalian brain
like eye movements ) this is feasible
- Generally have learned lot by studying complete system w output compared with purely
sensory system
Motor control & Feedback
- Feedback using info about result to improve performance is important in control of
movement
No Feedback: Ballistic control
- Many circumstances where motor system is forced to act blindly b/c for one reason or another
they are deprived of normal sensory feedback e.g. tossing orange peel into a waste bin
once it leaves hand & no sensory feedback helps w/ trajectory
o So have to work it before hand (e.g. the muscular contraction)
o classic e.g. is nest-building behaviour of brown rat (by Lorenz) once it decided to
build , it goes through stereotypic movements even if there is no material left to finish it
- Motor type of this act called ballistic (thrown) can be drawn in diagram
o Desired results (or goal) - e.g. orange peel into basket this is translated by controller
into appropriate pattern of commands
o These commands then produce the actual result through their effect on plant (i.e.
muscles)
o How well actual result compare with desired results depends on how good the
controller is more it knows about how plant will behave in response to any particular
command , the better it will perform - it needs a library of motor programs
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E.g. ballistic missiles
- But the this system has flaw it vulnerable to noise noise is any kind of unpredictable
disturbance that makes actual result differ from what the controller expects (e.g. wind)
- World is unpredictable particular pattern of activation in motor nerves will produce diff
movements of limbs depending on host of internal factors (e.g. temperature, fatigue etc.)
- More important effect of load when using limbs , given degree of muscle activity will
generate quite different movements depending what you have (e.g. feather vs. rock)
o Most of lower levels that control limbs are devoted to solving noise introduced by
unpredictable load
Parametric adjustment: Feed-forward & Feedback
- One way of dealing w/ noise to have some kind of sensor that monitors the noise before it
affects system & to use this info to adjust parameters of controller to allow for it
o Is called parametric feed-forward controller parameters to anticipate the effects of
noise e.g. adjusting for wind before launching the missile
- Much of info is used by the brain in this way especially for allowing different load e.g. neural
circuits controlling muscle length use info from force-detectors in the skin & tendons that make
appropriate adjustments of motor commands
- This is system also has flaw there are infinite of things can cause perturbations & brain cannot
have plan for every one of them in advance so approach is to have system that learn from its
own mistakes parametric feedback
- Need comparator compares actual result w desired results by subtracting one from another
if generates error singal that is used to modify controllers parameter
o Advantage to feedback is its flexibility rather than having stored program ready in
advance for anything can have rather simple all-purpose programs that maybe
redefine via trial & error for needed task that are actually encountered
- such that great deal of learning motor skills can be thoughts as parametric feedback in which
errors is used to modify our stored motor programs - e.g. playing darts or cricket
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Document Summary

Generally have learned lot by studying complete system w output compared with purely sensory system. Feedback using info about result to improve performance is important in control of movement. But the this system has flaw it vulnerable to noise noise is any kind of unpredictable disturbance that makes actual result differ from what the controller expects (e. g. wind) World is unpredictable particular pattern of activation in motor nerves will produce diff movements of limbs depending on host of internal factors (e. g. temperature, fatigue etc. ) One way of dealing w/ noise to have some kind of sensor that monitors the noise before it affects system & to use this info to adjust parameters of controller to allow for it. Is called parametric feed-forward controller parameters to anticipate the effects of noise e. g. adjusting for wind before launching the missile. Need comparator compares actual result w desired results by subtracting one from another.

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