Pre-Programmed Reactions

Dr: Sh.T. Boroujeni

Masoud Zahiri

In the name of Allah

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Pre-Programmed Reactions

Definition and origins of preprogrammed reactionsElements of historySensory source ofpreprogrammed reactionsComplex nature ofpreprogrammed reactionsExamples of commonly studied preprogrammed reactions

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An unexpected perturbation of a joint gives rise to a sequence of EMG events in a stretched muscle. The first one (M1) comes at a short latency (under 40 ms). Then two peaks (M2 and M3) come at a latency of between 50 and 100 ms. M2 and M3 are addressed as pre-programmed reactions. Later, a voluntary correction comes.

EMG

Time

Perturbation

M1

M2 M3

Voluntaryreaction

Definition Pre-Programmed Reactions

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Elements of history

PPR were first discovered in humans and only later in animals

The first study Hammod(1954)In particular, they have been studied in humans

during such tasks as maintaining a joint (limb) posture, performing a quick joint movement, walking, standing, gripping an object, and speaking.

Pre-Programmed Reactions

Also called triggered reactions, M2–M3, functional stretch reflex, transcortical reflex, long-loop reflex

Come at an intermediate latency (40–100 ms) Are involuntary in nature but can be modified by

instruction Can be triggered by stimuli of virtually any modality Generate a quick, crude compensation for the

perturbation Are followed by voluntary corrections

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R. A.Schmidt

Definition Pre-Programmed Reactions

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Pre-programmed reactions demonstrate a strong dependence on the instruction.If the subject is instructed to resist perturbations, the pre-programmed reactions are large (solid lines). If the subject is asked to let the limb move,the pre-programmed reactions are much smaller (dashed lines). Note that the M1 reaction is the same.

Effect of Instruction on MuscleReactions to a Perturbation

EMG

Time

Perturbation

M1

M2 M3

Voluntaryreaction

ReactLet go

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A subject is holding a position in a joint against a load with a central command to a muscle. If the subject knows that a perturbation can occur, he/she can prepare an addition to the central command that would compensate for the predicted perturbation. The pre-programmed command (∆C) is triggered by peripheral signals generated by the perturbation and attenuates the mechanical effects of the perturbation.

A Possible Scheme

Muscle

Central command

Tonic stretch reflex mechanism

∆C

Afferents

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The actual source of the triggering signal for a pre-programmed reaction is not important as long as the signal carries sufficient information. It can be provided by proprioceptors, a flash of light, a loud tone, etc.

Pre-Programmed Responses Can Be Triggered by Any Sensory Signal

Muscle

Central command

Tonic stretch reflex mechanism

∆C

Proprioceptors

Vision

Hearing

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If a perturbation occurs during a fast voluntary movement, EMG changes are seen at a characteristic for the pre-programmed reactions latency. Generally, they involve an increase in the activity of a muscle that acts against the perturbation, and a decrease in the activity of a muscle that is assisted by the perturbation (bold lines).

Effects of a Perturbation AppliedDuring a Fast Movement

agonist

antagonisttime

EMGan increasein load

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Muscle vibration has different effects on different components of the responses to an external perturbation. The early response (M1) is suppressed just like the H-reflex, whereas the pre-programmed response (M2-M3) is unchanged.

Effects of Vibration on M1-2-3

Responses

Vibration

EMG

TimePerturbation

M1 M2-M3

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Examples of commonly studied preprogrammed reactions

1) Classical (lab conditions)

2) Grip Reactions

3) postural perturbations (ankle and hip strategies)

4) Preprogrammed Reactions in Locomotion

“Corrective stumbling reaction”

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One ofthe most commonly used methods to study preprogrammed reactions is to ask a subject to hold a position in a joint against a bias extemalload and then to change the load quickly.

Classical (lab conditions)

Pre-programmed postural corrections to a perturbation created by platform movement are context-dependent. If the cup is loaded with play dough, the corrections will be different than if the cup is full of hot tea.

Effects of Intentionon Quick Muscle Reactions

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Grip reaction

mechanical or electrical stimulation of the paw during locomotion induces different reactions in the swing and the stance phases. In the swing phase (A), there is a flexor reaction, so that the leg steps over a fictitious obstacle. In the stance phase (B), there is an extensor reaction, leading to the shortening of the stance phase for this limbA.

Corrective Stumbling Reaction

Surface

StimStim

A B

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Corrective stumbling reaction:

Preprogrammed Reactionsin Locomotion

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Occurs during locomotion

Can be induced by a mechanical stimulus to the foot

Represents a complex pattern of EMG changes

Leads to a quick step over the obstacle

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postural perturbations (ankle and hip strategies)

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Debra J. Rose,References

Richard A. Schmidt, WRISBERG LATSH

Thank you for your attention

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