PHASIC MODULATION OF VESTIBULOSPINAL NEURON ACTIVITY DURING FICTIVE LOCOMOTION IN LAMPREYS

This study was aimed at characterizing the activity of vestibulospinal neurons recorded intracellularly during fictive locomotion in lampreys. The majority (78%) of identified vestibulospinal neurons showed rhythmic fluctuations of their membrane potential correlated with locomotor discharges recorded in pairs of rostral ventral roots. Of the rhythmically modulated vestibulospinal cells, most (72%) were maximally depolarized during ipsilateral ventral root discharges and showed a minimum during contralateral activity. Other cells (20%) showed an opposite pattern, that is their peak of depolarization occurred during contralateral activity. Finally, a third category of cells (8%) showed a more complex pattern of activity. Two waves of depolarization could occur per locomotor cycle, one during each burst discharge. The pattern of fluctuation recorded in vestibulospinal neurons appears to be related to the side of the spinal cord onto which the cells are projecting.