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Motor prediction (Disorders of control and awareness (not important)…
Motor prediction
Disorders of control and awareness (not important)
Schizophrenia
deficit in predicting sensory consequences of own actions
less attenuation of self-regerated sensation
passivity experiences
actions not directed by themselves
abnormality in forward model prediction
difficulty destiguishing between correct visual feedback and false feedback
no decrease in perceptual ratings of stimuli produced by themselves
abnormality in foreward model
Awareness of motor system
aware of goal and state of action
unaware of fine adjustments
unaware of results of comparison if desired state is successfully achieved
Optic ataxia
difficulty grasping objects
aware of problems
inverse models are not properly tuned by context
Anarchic hand sign
hand moves without will
recognize discrepancy
representations activated inappropriately
Utilization behavior
damage in frontal lobes
stereotyped action inappropriate to the context
unaware of discepancy action-intention
rationalization
early stage in development of action
Phantom limb
can initially be moved but this goes away
limb position also based on motor commands
forward models become modified and reduce discepancy
Fading limb
unaware of limb without visual feedback
system learns to estimate on visual signals and motor commands
Anatomy (not important)
cerebellum
tactile attenuation
activity in right anterior cerebellar cortex is reduced when tactile stimulus is self generated
predictive cancellation signal
forward model system
predict consequences of planned action
learning and maintaining internal models
Purkinje cells
receive input from parallel fibers/climbing fibers
transformation from parallel to purkinje may implement an internal model
predict sensory feedback
signals error
Parallel fiber
signal desired movement goal
climbing fiber
signal discepancy between expected and actual sensory input
training signal
M1
motor adaptation
Somatosensory
activity attenuated by self-produced sensory stimuli
secondary somatosenory cortex
increase with external tactile stimulus
also in anterior cingulate gyrus
how does the brain make predictions
Wolper & ghahramani
Internal model
curse of dimensionality
exponential increase of storage and calculations
context
descrete/slowly changing parameters
modelling sensorimotor system
Sensorimotor loop
3 stages
specify motor command
inverse model
determine how state changes given motor command
forward dynamic model
specify sensory feedback given new state
forward sensory model
Tasks
Motor planning
optimal control
cost
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maximizing smoothness
minimize volume of ellipsoid
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selection problem
depends on dynamics of limb and the environment
motor command
alpha neurons
cortical motor neurons
encode all movement properties
State
estimation and prediction
current stat
2 problems
delay of transduction of sensory signal
noise
observer
using sensory feedback and forward models to estimate current state
example
Kalman filter
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context
estimation
bayserian approach
estimate probability of each context
likelyhood
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prior
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Learning
internal models must be adaptable to changes in the system
error signal
difference between predicted and sensory feedback
used for updating
are sensory and first need to be converted into motor
feedback error learning model
if feedback produces no motor command then no discepancy so good prediction
repersent aspects of own body and interaction with the external world in order to optimize motor control and learning
Noise
leads to uncertainty
minimizing uncertainty
combining multiple signals with prior knowlegde
some body states are more likely
bayesian framework
strength of belief
predictive filtering
removing less informative signals
mechanisms
presynaptic inhibition of primary afferents by central command signal
sensory
motor
optimal control
environmental
inverse model
What is the difference between the two types of processing
forward internal models
motor to sensory transformation
predict behavior of body and world
internal representation of environment used to transform the efference copy signal into a sensory prediction
electric fish
sensory cancellation?
when one body part touches other
2 types of predictions
actual outcome of motor command, compared to desired outcome
predict sensory consequences of movement, compare with actual feedback
causal relationship between action and outcome
Inverse internal models
from sensory to motor transformation
provides motor commands necessary to achieve desired outcome
Why does the brain make predictions
to distinguish between sensory consequences of own actions from external actions
Why cant you tickle yourself