Lecture 9b, Open-Loop Control & Motor Programs (2) Flashcards
Deafferentation & Movement Blocking
healthy control: the EMG the agonist muscle comes on to move the limb closer to the target then the antagonist comes on supposedly to break the movement and then followed by a second agonist burst to clamp the movement
deafferented patient: should look the same if this movement is programmed and is not dependant on proprioceptive feedback
Start-React Effect
acoustic startle response
- startle indicator in human is sternocleidomastoid (SCM) contraction (NECK clenching) - can tell if they have been startled by this
- a loud (>90 dB) acoustic stimulus (louder is better); results in characteristic set of muscle responses
for comparison: City traffic ~80 dB; hand-drill ~98dB, lawnmower ~105bB, rock concert ~115dB
◦ anything louder than 90dB can
startle someone
- can be used as a method to try and determine whether people pre-program in response or whether we can use the startle response to kick out any programming in advance
- does it act as a go signal (the startle) and act as a prepared response
- we have something ready in package; this can be elicited at quick interval just by a loud stimulus
Startle Response in person exposed to 124dB tone (passive – non preparing to move)
- very early responses ~50-70ms (the blink and clinching response) - suggests that it is reflexive
- the person is just passive so nothing in biceps to triceps
Triphasic EMG pattern in typical control trial
- on average, premotor RT = 95 ms
- triphasic pattern
- SCM and OOc nothing is going on because they have not been startled
- EMG comes on before displacement begins
Triphasic EMG pattern in a typical startle trial
- on average, premotor RT = 64 ms (comes on really early)
- triphastic pattern in triceps and biceps
- startle indicators are on (neck and eye blink)
- reacting extremely fast to this startle sound
Start-React effect and motor programs
- the start-react effect is when a loud, startling tone results in a startle response and releases whatever movement is prepared (the motor program) with a much-reduced RT
- the startle triggers the specific prepared movement, just much faster
How do we know that the StartReact effect is not just an extreme example of a stimulus intensity effect?
- but when startled (SCM activity), RT insensitive to stimulus intensity
- when people are startled we see very fast reaction times, the RT are not sensitive to stimulus intensity when startled
- the start react effect is not just stimulus intensity effect it is something else, the suggestion is you are bypassing stages and reflexive like response to this auditory stimulus
Start-React effect: Hypotheses
stimulus intensity effect
1. startle response may increase excitability in nervous system and therefore result in shorter RTs
◦ NO (you need to have
something prepared)
subcortical trigger
2. sufficient detail of the movement is prepared in advance (pre-programmed) and susceptible to trigger via subcortical mechanism
◦ ✓ movement must be
prepared in advance in order
to be triggered
Start-React Effect Conclusions
because a startling acoustic stimulus (SAS) can trigger “pre-programmed” motor commands (simple RT tasks), but cannot trigger motor commands not programmed in advance (choice RT tasks), the Start-React effect provides evidence for the existence of motor programs