Stretch and unloading reflexes in cortically evoked movements of unanesthetized cats

Using the same experimental prodedure as we employed in the previous paper [5], extension and flexion cortically-evoked movements (CEM) about the elbow joint have been analyzed in unanesthetized cats by an external load disturbance method (ELD). These movements were evoked by intracortical microstimulation (ICMS) of the motor cortex. A combined quantitative analysis has been made of extension and flexion CEM and also motor reactions evoked by direct stimulation of the muscle antagonists, in unanesthetized animals. Determinations were made of the resulting stiffness at different stages of two sequential oppositely directed cycles of change in the external load, and of the uncertainty index (UI) of the disturbed movements. Depending on the relationship between the directions of the preceding and the disturbed movement, the CEM in the cyclical backwards and forwards external load changes were divided into two types: coincident (type 1), and opposite (type 2). If the preceding movement was evoked by ICMS, then disturbed movements (types 1 and 2) were a realization of phasic myotatic reflexes, the unloading and stretch reflexes, respectively. Type 1 disturbed movements are characterized by a rather narrow range of variation of the mean UI values (0.43–0.91 and 0.24–0.73 for frequencies of disturbance 1.2 and 3.2 Hz, respectively). The transition to type 2 CEM brought about a sharp increase in the scatter of mean UI values; they could be positive or negative, and the dispersion also increased significantly. It is suggested that the intensity of central processes of regulation of a disturbed movement are connected not so much with its continuous development, as with changes in its direction.