Faculty Bibliography

The vibrissal movements known as whisking are generated in a pulsatile, or non-continuous, fashion and comprise sequences of brief regularly spaced movements. These rhythmic timing sequences imply the existence of periodically issued motor commands. As inferior olivary (IO) neurones generate periodic synchronous discharges that could provide the underlying timing signal, this possibility was tested by determining whether the olivocerebellar system modulates motor cortex (MCtx)-triggered whisker movements in rats. Trains of current pulses were applied to MCtx, and the resulting whisker movements were recorded using a high speed video camera. The evoked movement patterns demonstrated properties consistent with the existence of an oscillatory motor driving rhythm. In particular, movement amplitude showed a bell-shaped dependence on stimulus frequency, with a peak at 11.5+/-2.3 Hz. Moreover, movement trajectories showed harmonic and subharmonic entrainment patterns within specific stimulus frequency ranges. By contrast, movements evoked by facial nerve stimulation showed no such frequency-dependent properties. To test whether the IO was the oscillator in question, IO neuronal properties were modified in vivo by intra-IO picrotoxin injection, which enhances synchronous oscillatory IO activity and reduces its natural frequency. The ensuing changes in the evoked whisker patterns were consistent with these pharmacological effects. Furthermore, in cerebellectomized rats, oscillatory modulation of MCtx-evoked movements was greatly reduced, and intra-IO picrotoxin injections did not affect the evoked movement patterns. Additionally, multielectrode recording of Purkinje cell complex spikes showed a temporal correlation of olivocerebellar activity during MCtx stimulus trains to evoked movement patterns. In sum, the results indicate that MCtx's ability to generate movements is modulated by an oscillatory signal arising in the olivocerebellar system

This article addresses the functional significance of the electrophysiological properties of thalamic neurons. We propose that thalamocortical activity, is the product of the intrinsic electrical properties of the thalamocortical (TC) neurons and the connectivity their axons weave. We begin with an overview of the electrophysiological properties of single neurons in different functional states, followed by a review of the phylogeny of the electrical properties of thalamic neurons, in several vertebrate species. The similarity in electrophysiological properties unambiguously indicates that the thalamocortical system must be as ancient as the vertebrate branch itself. We address the view that rather than simply relays, thalamic neurons have sui generis intrinsic electrical properties that govern their specific functional dynamics and regulate natural functional states such as sleep and vigilance. In addition, thalamocortical activity has been shown to be involved in the genesis of several neuropsychiatric conditions collectively described as thalamocortical dysrhythmia syndrome

The electrophysiological properties of rat inferior olive (IO) neurons in the dorsal cap of Kooy (DCK) and the adjacent ventrolateral outgrowth (VLO) were compared with those of IO neurons in the principal olive (PO). Whereas DCK/VLO neurons are involved in eye movement control via their climbing fiber projection to the cerebellar flocculus, PO neurons control limb and digit movements via their climbing fiber projection to the lateral cerebellar hemisphere. In vitro patch recordings from DCK/VLO neurons revealed that low threshold calcium currents, Ih currents, and subthreshold oscillations are lacking in this subset of IO neurons. The recordings of activity in DCK neurons obtained by using voltage-sensitive dye imaging showed that activity is not limited to a single neuron, but rather that clusters of DCK neurons can be active in unison. These electrophysiological results show that the DCK/VLO neurons have unique properties that set them apart from the neurons in the PO nucleus. This finding indicates that motor control, from the perspective of the olivocerebellar system, is fundamentally different for the oculomotor and the somatomotor systems