Feedforward & Feedback Control of Movement - Lecture 3

the nervous system uses what 2 main strategies to control movement?

1. feedback control

2. feedforward control

feedback control

movement corrections guided by/based on sensory input (visual, proprioceptive, tactile) during/after movement

characteristics of feedback control

- reactive: relies on error detection

- slower than feedforward due to sensory processing delays & sole reliance on feedback

- essential for accuracy in unpredictable movements

visual feedback example

vision, trajectory of a ball, etc.

proprioceptive feedback example

when movement is being performed

tactile feedback example

making sure ball makes contact with center of hand instead of thumb

feedback control lecture example

- adjusting hand trajectory when catching ball after it bounces unexpectedly

*it uses visual info to obtain visual feedback to change trajectory*

feedforward control

anticipatory motor commands/predictive adjustments made before movement occurs

*based on prediction; tries to guess what the right thing would be*

feedforward control information comes from where?

the brain & goes down the spinal cord; it is entirely MOTOR & MEMORY

feedforward control characteristics

- proactive: no reliance on real-time feedback

* advantage of this is it anticipates needs i.e. being proactive this semester rather than reactive*

- faster, but dependent on prior experience & internal models

- crucial for coordination & postural adjustments

internal models in feedforward control refers to

internal memory of precise movements necessary to achieve a task

feedforward control example

activating trunk muscles before lifting a heavy object

both types of control (feedback & feedforward) operate ____ for ____ and ____ actions. Both are stored in the ______ & communicate with the _____.

together; smooth; accurate; cerebellum; primary motor cortex

feedforward ______ & _______ demands

initiates; anticipates

feedback ______ & _____ ongoing action as its going through process

monitors; corrects

optimal motor control

predictive planning + sensory based corrections; is a smooth continuous motion that achieves the wanted task

integration in motor control clinical relevance

motor impairments often reflect deficits in one or both systems

- example: cerebellar damage impairs feedforward; sensory loss impairs feedback & some motor action

blindfolded + unknown weight catching demonstrates interaction?

- interaction between feedforward (anticipatory) and feedback (reactive) control

regarding blindfold + unknown weight catching, without vision, the system relies on what?

system solely relies on prediction/anticipation + proprioceptive/tactile input; it removes feedforward preparation & feedback adjustments in real time

unknown weight exposes what limits?

limits of feedforward, thus requiring feedback correction

what are the brain areas involved in feedforward control (anticipatory)

- prefrontal cortex

- premotor cortex & SMA

- basal ganglia

- cerebellum

- primary motor cortex

prefrontal cortex

sets intention i.e. prepares to catch (what is it that we want to do)

premotor cortex & somatosensory association cortex

plans anticipatory posture & arm movement

example: what must you do in order to resist the weight of a ball

basal ganglia

selects motor program; excitation/activation of certain muscle roots & inhibition of the rest

cerebellum

predicts required muscle activation; i.e. sends info to primary motor cortex needed/that is required to catch the ball

primary motor cortex

sends commands to alpha motor neurons; i.e. a low level of stimulation getting ready to catch the ball

what are the descending motor tracts involved in feedforward control (anticipatory)

- corticospinal (lateral)

- reticulospinal

- vestibulospinal

- rubrospinal

corticospinal (lateral)

fine hand/finger control

reticulospinal

anticipatory postural adjustments

example: in regards to being able to resist weight added to front of body when catching a ball

vestibulospinal

balance/head stability

rubrospinal

hand shape & upper limb flexor readiness

example: ability to fire at the moment of contact with ball

what are the peripheral receptors involved in feedback control (reactive) sensory systems

- cutaneous touch/pressure receptors

- muscle proprioceptors

cutaneous touch/pressure receptors

- impact & grip i.e. pacinian, Ruffini, merkel, meissner (touch, vibration, stretch cutaneous receptors)

muscle proprioceptors

- muscle spindles: detect stretch

- golgi tendon organs: detect tension

muscle spindles are activated when?

when suddenly stretched

golgi tendon organs inform what?

inform CNS which then informs brain

example: CNS informs brain on how heavy the object is

what are the ascending sensory tracts involved in feedback control (reactive) sensory systems

- fine touch & proprioception --> primary somatosensory cortex

- unconscious proprioception ---> cerebellum

what are the 2 places proprioception goes?

1st = cerebellum --> unconscious adjustment

2nd = primary somatosensory cortex

*sensory info needs to be received & perceived in order to make adjustments*

example: if you knock someone out & ask them where their left foot is they would know (i.e. conscious awareness) unless their primary somatosensory cortex is damaged.

what are the descending corrections involved in feedback control (reactive) MOTOR systems

- corticospinal

- reticulospinal & vestibulospinal

corticospinal descending corrections

cortical corrections to grip/trajectory

reticulospinal & vestibulospinal descending corrections

rapid tone/ postural control; shifts center of gravity

muscle stretch reflex

fastest response w/o any contribution from the brain, but it will later go up into brain to later produce conscious awareness

what are the reflexes (fast control mechanisms) involved in feedback control (reactive) MOTOR systems?

- spinal stretch reflex

spinal stretch reflex

initiated by activation of muscle spindles; happens behind the scenes

what is the outcome of feedback control (reactive) MOTOR systems?

adjusts grip & arm force to match true weight

feedforward descending tracts

fast, predictive BUT error prone i.e. EXPECTATION

feedback (ascending + descending tracts)

slower, precise corrections i.e. REALITY

what type of info comes from the cerebellum?

expectation vs. reality; proprioceptive info also comes from cerebellum

cerebellum is the ________. It compares _____ vs _____. It ____ motor programs via _________ to _____ cortex.

central hub; predicted vs. actual; updates motor programs ; connections to motor cortex

clinical relevance of integration of feedforward & feedback

- corticospinal damage

- cerebellar damage

corticospinal damage

poor fine motor correction

cerebellar damage

failed predictions, clumsy reliance on feedback (loss of proactiveness & prediction)

TRUE OR FALSE: image to sensory areas can also contribute to motor damage

TRUE