Operant Conditioning of the Human Soleus Short Latency Stretch Reflex and Implications for the Medium Latency Soleus Stretch Reflex

Abstract

The human soleus stretch reflex is comprised of several components with different latencies typically termed the SLR, MLR and in some cases LLR component. The SLR is suggested to be mediated by Gr Ia afferent arising from activation of spindle afferents, the MLR is predominantly due to gr Ib and II feedback while LLR likely contains a cortical component. Here we report data on the changes in both the SLR and MLR following a well-established conditioning protocol. Participants attended 30 sessions where the initial six served as a baseline measure of reflex size and the following 24 sessions were devoted to training the participants to either increase or decrease the SLR component. Following successful up-conditioning of the SLR, the MLR remained unchanged. However the SLR and MLR both decreased with down-conditioning. This suggests that the MLR is not exclusively Gr Ib or II based but has some Ia afferent input.