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

Purpose: Successful operant conditioning of the biceps brachii spinal stretch 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 using operant conditioning and to observe any concurrent change in the SSR. Methods: Fourteen, able-bodied, human subjects were randomly assigned to either the control group or the training group. The LLRR and SSR responses were measured as magnitude of electromyographic response to a quick stretch of the elbow flexors, delivered by a torque motor. All the subjects attended fourteen sessions. The first six sessions were baseline sessions during which 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 eight sessions for the training group comprised the operant conditioning. Results: Operant conditioning of the LLRR resulted in a statistically significant 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 uncoupling 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 responses can be volitionally uncoupled.