The influence of adequate vestibular stimulation on evoked locomotor muscle activity in the decerebrated guinea-pig.

The influence of adequate vestibular stimulation on locomotor muscle activity has been investigated in the decerebrated guinea-pig. Locomotor activity was evoked by electrical stimulation of the mesencephalic locomotor region, whose location has been ascertained in this animal. Vestibular stimulation was performed by cyclic tiltings about the longitudinal and transverse axes and swinging along the vertical axis. The translation frequency was in the range of 0.02-0.8 Hz with an amplitude of +/-20% for tilting and 40 mm for swinging. Vestibular stimulation was accompanied by distinct changes in locomotor electromyographic activity of fore- and hindlimb antagonist muscles. During stimulation the intensity of discharges in extensor and flexor muscles corresponding to the stance and swing phases of the locomotor cycle was modulated; the alternation of antagonist muscle activity was not as a rule disturbed. The changes in muscle activity had the same pattern and similar phase-frequency properties to those observed under analogous vestibular stimulation during the maintenance of steady posture. It is suggested that the vestibular system is of considerable importance for the regulation of locomotor muscle activity. During locomotion the vestibular system influences mainly spinal motor output but does not act on the locomotor generator.