1994 Volume 43 Issue 5 Pages 352-360
Premovement facilitation of spinal monosynaptic reflex was investigated under different movement modalities using both visually guided tracking movement and the H-reflex technique. Subjects performed fast step and slow ramp movements under reaction time (RT) conditions and self time determining (Self) conditions. For each of the conditions, the motor task was bilateral simultaneous dorsiflexion.
Under both RT and Self conditions, the onset of premovement H-reflex facilitation (OPHF) was significantly prolonged in the slow ramp movement (RT, 37, 3±11.8 ms ; Self, 79.4±21.8 ms) compared with the fast step movement (RT, 24.4+6.2 ms ; Self, 43.4±14.2 ms) . In addition, OPHF was significantly prolonged under Self conditions in both the step and ramp movements. Movement time (MT) did not differ significantly under RT and Self conditions except in three subjects. The peak value of torque change (PV) was larger under Self conditions than under RT conditions in four out of ten subjects.
From these results, we conclude that OPHF is modulated not only by changes in movement speed but also by changes in movement modality. It is suggested that this contextual dependency of OPHF might be controlled by the supraspinal motor center.
