Lecture 9b, Open-Loop Control & Motor Programs (2)

Question 1

Deafferentation & Movement Blocking

Answer 1

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

Question 2

Start-React Effect

Answer 2

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

Question 3

Startle Response in person exposed to 124dB tone (passive – non preparing to move)

Answer 3

• 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

Question 4

Triphasic EMG pattern in typical control trial

Answer 4

• 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

Question 5

Triphasic EMG pattern in a typical startle trial

Answer 5

• 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

Question 6

Start-React effect and motor programs

Answer 6

• 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

Question 7

How do we know that the StartReact effect is not just an extreme example of a stimulus intensity effect?

Answer 7

• 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

Question 8

Start-React effect: Hypotheses

Answer 8

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

Question 9

Start-React Effect Conclusions

Answer 9

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