Motor control strategies underlying head stabilization and voluntary head movements in humans and cats

Strategies for movement and stabilization of the head were examined within several paradigms tO determine which CNS mechanisms were responsible. Patterns of muscle activation were observed during the performance of reflex (head-fixed) and voluntary (head-free) movements in the cat. Spatial patterns of human neck muscles were also observed during ap isometric head stabilization task. Both studies indicated that, although the neck muscles have the potential to respond in multiple directions, fhey were actually programmed to respond maximally in a single preferential direction that was task, dependent. Measures of head position, head velocity,; and EMG response during rotations of the body about the vertical axis suggested a predominance of vbluhtarily organized responses at low frequencies with the possibility of participation of the vestibular reflexes at frequencies in the rang of 1 to 5 Hz