Changes in electromyographic responses to muscle stretch, related to the programming of movement parameters.
Three experiments are reported that used the advance information paradigm which consists of providing subjects with either no or partial information about an upcoming movement. Subjects moved handles to control the vertical displacements of CRT beams, to point to eight targets. The illumination of different combinations of these targets prior to movement execution provided advance information about which hand, movement direction, or movement extent would be required. Reaction time (RT), integrated EMG activity in the forearm extensor and flexor muscles, and M1, M2, and M3 components of the stretch reflex responses triggered in these muscles were analysed as a function of the precued movement parameter. Compared to the no-information condition, RT decreased in all precue conditions; however, the reduction was greater when direction than when hand was precued, and greater when hand than extent was precued. The EMG activity of forearm muscles increased during the preparatory period in all precue conditions, but generally did not differ among them. An overall facilitation of the stretch reflex components was observed in all precue conditions. This facilitation: (1) was greater for flexor than extensor muscles, (2) was similar regardless of the degree of extent precued, (3) differed for the M2 and M3 components depending on whether the responding hand precued was ipsilateral or contralateral. When the precued movement direction was considered, similar changes in the M3 component were found in extensor and flexor muscles. M3 was facilitated when the muscle was precued as an agonist and was inhibited when it was precued as an antagonist. Collectively these data provide support for a motor programming conception of movement organization.