Step cycle-related oscillatory properties of inferior olivary neurons recorded in ensembles

This study was conducted to characterize patterns of discharge from the dorsal accessory olive during different behavioural states. To accomplish this goal, adult rats were chronically implanted with arrays of microwires (25-50 microns) to record from as many as 23 neurons from the dorsal accessory olive bilaterally during locomotor paradigms or at rest. Olivary neurons discharged sporadically at low firing frequencies (1-5 Hz) when the rat was at rest. However, during locomotor paradigms involving constant speed treadmill locomotion, olivary neurons discharged rhythmically at frequencies which closely matched step cycle frequencies. The rhythmic nature of olivary discharge was maintained even during brief periods of inconsistent gait. During treadmill locomotion utilizing variable acceleration/deceleration paradigms olivary neurons discharged at 3 Hz frequencies. Electrical stimulation of peripheral afferents resulted in rhythmic discharge of olivary neurons at frequencies harmonic with the rate of stimulation. These data suggest that oscillatory patterns of discharge exhibited by the inferior olivary nucleus are only seen during rhythmic behavioral tasks or stimulation paradigms. Further, the dissociation between the rhythmic nature of the task and the continued oscillation suggests that oscillatory activity of the inferior olive may be due both to an intrinsic rhythm as well as related to ongoing sensorimotor input.