L9B: Motor Programs

Question 1

How do Blocked movements & the Triphasic pattern of
Muscle Activation (agonist & antagonist) support the existence of motor programs?

Answer 1

1. Initial Activation (AG1): The agonist (AG1) muscle fires first, initiating movement. The activation begins around the 0 ms mark (contraction to initiate the action)
2. Antagonist Inhibition (ANT): After the initial agonist activation, the antagonist muscle (ANT) briefly activates in an inhibitory manner, preventing unwanted resistance to the movement (this phase corresponds to the negative voltage spike in the graph). This step is crucial for smooth motion, allowing the agonist to move freely without opposition from the antagonist.
3. Reactivation of the Agonist (AG2): After the antagonist’s brief inhibition, the agonist (AG2) fires again to sustain the movement or to provide a final push.

Watch Lecture

• The blocked movements suggest that the planned action is momentarily halted, possibly due to an external cue or task constraint. During this period, the brain may adjust the motor commands or refine the motor program, maintaining a state of muscle readiness for when the movement is unblocked.
• The triphasic pattern helps in producing efficient movement by ensuring that the antagonist muscle’s action is appropriately timed and counterbalanced by the agonist’s contractions, preventing unnecessary resistance or erratic movements.

Question 2

Why do we get this triphasic EMG pattern? Is it part
of the motor program or based on feedback?

Answer 2

1. Agonist 1 (AG1)
   Main impulse for the movement Precedes movement onset (takes time to overcome inertia)
2. Antagonist (ANT)
   Thought to represent “braking” (decelerate limb)
3. Agonist 2 (AG2)
   Helps to clamp limb at target Co-contraction

Question 3

What is the Blocking paradigm?

Answer 3

In the blocking paradigm, where the movement is physically blocked during a prepackaged motor program, the expected response is that the triphasic pattern would be disrupted.

When movement is blocked:
- If the motor program was prepackaged, the agonist muscles would still fire, but the antagonists would likely co-contract in an attempt to produce the planned movement, as there is no feedback to adjust the movement.
- The correct answer is: d

Question 4

Triphasic pattern was still observed (blue trace),
almost identical onset and amplitude of antagonist

Answer 4

Question 5

What caused the Antagonist muscle burst to “turn on” even though the movements were blocked?

Answer 5

The motor program

If the movement is blocked at initiation, we would not need the antagonist burst (to decelerate/slow the limb) & agonist2 to “clamp” it in place

Question 6

What would happen if Ian Waterman (deafferented
person) did this blocking study?

Answer 6

We would still see the triphasic pattern

Question 7

What can we conclude about the
triphasic pattern?

Answer 7

• If the movement is prepackaged in advance and controlled by the motor program then we would see the triphasic pattern
• Feedback was not necessary to produce this simple fast aiming movement
• Pattern of muscle commands was not a response to proprioceptive feedback

Question 8

How does the Start-React effect provid evidence for motor programs?

Answer 8

The start-react effect is when a loud, startling tone
results in a startle response AND any prepared response.

The startle acts as a “go” to release whatever movement
is prepared (the motor program) with much-reduced RT.

Question 9

What is the acoustic startle response?

Answer 9

A loud (>90 dB) acoustic stimulus (louder is better); results in characteristic set of muscle responses.

Primary startle indicator in humans is the sternocleidomastoid (SCM) contraction (NECK clenching)

Question 10

Startle Response in person exposed to 124dB tone
(passive – not preparing to move)

Answer 10

Very early responses: ~50-70ms (reflexive like responses)

Question 11

What would we expect in startle trials when
person ready to make extension movement?

Answer 11

C = Startle response and extension movement earlier in time (faster RT)?

both at same time

Question 12

Answer 12

Question 13

Start-React effect and motor programs
(summary slide)

Answer 13

Question 14

Answer 14

Question 15

Would we see the start-react effect (faster RTs) in CRT
situations of 2 or 4 choice?

Answer 15

We only see start-react effect when movement can be
prepared in advance. This is not possible in CRT task

Question 16

Can sprinters take advantage of the startle response “start-react effect” when reacting to a loud starter’s gun?

Answer 16

“… IAAF regulations governing athletic running events state that reactions faster than 100 ms must be regarded as anticipation of the starting signal, and therefore classed as a false start. Several of our subjects started leg movement within 100 ms of the startling noise, suggesting that this limit may need revision.”

Question 17

Summary part II

Answer 17