[Muscle stretching and unloading reflexes during cortically evoked movements in unanesthetized cats]

Extension and flexion cortically-evoked movements (CEMs) were studied in the framework of the experimental approach developed in the previous paper [5]. Movements in the elbow joint of an unanesthetized cat were evoked by intracortical microstimulation (ICMS) applied to the motor cortex, then they were tested using a torque disturbance method. Similarity of flexion and extension CEMs allowed producing their combined quantitative analysis and comparing the obtained characteristics with those defined for the movements which were evoked by direct stimulation of the biceps and triceps muscles in an anesthetized animal. Resulting stiffness and uncertainty index (UI) served as the main characteristics of the movement in the presence of torque disturbances. Depending on the relationship between the directions of the preceding movement and the initial phase of the disturbed one, CEMs were divided into two types: coinciding (1) and opposing (2) CEMs. When the preceding movement was evoked by switching on of ICMS, both types of the disturbed movements could be considered as realizations of the phasic myotatic reflexes: unloading (1) and stretch (2). Disturbed movements of type 1 were characterized by the narrow range of mean values of UI: 0.43-0.91 (1.2 Hz wave of torque disturbance) and 0.24-0.73 (3.2 Hz). Transition to type 2 enlarged sharply the spread in the means, they could be both positive and negative, variances of UI in separate realizations significantly increased as well. It is supposed that intensity of central processes controlling the disturbed movements is mainly connected with changes in their direction but not with the movement per se.