Stretch evoked potentials and M2 reflexes

Abstract

Reflex mechanisms are an efficient method humans use to deal with mechanical disturbances in daily life. In the muscle we see two reflexes, the M1 reflex and the M2 reflex. The M2 reflex is cortically modulated and is affected by intention
and habituation. A lot of research has been conducted on understanding the M2 reflexes, their origin and the factors influencing these reflexes. Less research, however, has been done to understand the cortical contribution of these M2 reflexes and what affects the muscle stretch evoked potentials. This research investigates the relationship between the stretch evoked potential and the corresponding M2 reflexes. We investigate the effects of the traditional ’Resist’ and ’Let Go’ tasks with a wrist manipulator on the evoked potential and M2 reflex, as well as the effect of longer periods between perturbations. This research showed that between the ’Let Go’ and ’Resist’ tasks, no difference in evoked potentials were present. There was a difference in the late M2 reflex however. The evoked potential was affected by the time between perturbations. A higher time between perturbations elicited a higher cortical response at the motor cortex as well as a higher M2 reflex. This result suggests that besides the task goal, the habituation and time between perturbation can be a significant factor at both the muscle as well as cortical levels. These results facilitate more elaborate research where the effect of these factors is investigated during voluntary movements.