HUMAN MUSCLE-SPINDLE AFFERENT ACTIVITY IN RELATION TO VISUAL CONTROL IN PRECISION FINGER MOVEMENTS

1. Impulse activities of muscle spindle afferents from the finger exte nsor muscles were recorded in the radial nerve of human subjects. In a ddition to single unit activity, surface EMG was recorded as well as f inger joint position and angular velocity. 2. All units were studied u nder two conditions of voluntary finger movements. In the visual condi tion, the subject tracked ramp and hold sequences at a single metacarp ophalangeal joint. In the non-visual condition the subject was asked t o produce the same movement while visual control was denied altogether . 3. With sixteen units, detailed statistical analyses failed to revea l significant differences in muscle spindle afferent activity between the visual and the non-visual task. However, with two group Ia units, impulse rate was marginally but significantly higher in the visual tas k even when differences in average movement velocity, velocity variabi lity and EMG level had been factored out. 4. The findings suggested th at access to visual information for movement control did not produce a ny large-scale differences in spindle afference, although a small effe ct of an increased and independent gamma-activation emerged in the sta tistical analysis in 11 % of the units.