Uncoupling of human short and long latency stretch reflex responses with operant conditioning

Purpose: Successful operant conditioning of the biceps brachii spinal stret ch reflex (SSR) has resulted in concurrent changes in the magnitude of long latency reflex responses (LLRRs). This finding suggests a coupling of the SSR and LLRR. The purpose of the present study was to downtrain the LLRR us ing operant conditioning and to observe any concurrent change in the SSR. Methods: Fourteen, able-bodied, human subjects were randomly assigned to ei ther the control group or the training group. The LLRR and SSR responses we re measured as magnitude of electromyographic response to a quick stretch o f the elbow flexors, delivered by a torque motor. All the subjects attended fourteen sessions. The first six sessions were baseline sessions during wh ich no conditioning or feedback occurred. The next eight sessions were the same as the baseline sessions (extended baseline sessions) for the control group; no feedback or operant conditioning of the LLRR occurred. The next e ight sessions for the training group comprised the operant conditioning. Results: Operant conditioning of the LLRR resulted in a statistically signi ficant reduction of that response within the training group and between the two groups. Also, operant conditioning of the biceps brachii LLRR did not result in concurrent changes in the magnitude of the SSR suggesting an unco upling of these responses. Conclusions: The LLRR of the biceps brachii could be operantly conditioned without significant changes in the SSR which suggests that these two respon ses can be volitionally uncoupled.