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The Journal of Neuroscience, June 15, 2003, 23(12):5264-5271
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State-Dependent Processing of Sensory Stimuli by Thalamic Reticular Neurons
Jed A. Hartings,
Simona Temereanca, and
Daniel J. Simons
Department of Neurobiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261
Inhibitory neurons of the thalamic reticular (RT) nucleus fire in two activity modes, burst and tonic, depending on an animal's behavioral state. In tonic mode, depolarized RT cells fire single action potentials continuously, whereas burst firing consists of grouped discharges separated by periods of quiescence. To determine how these firing modes affect sensory-evoked RT responses, single-unit responses to controlled whisker deflections were analyzed according to the burst versus tonic mode of spontaneous activity (SA) preceding the response. After burst mode activity (i.e., either quiescence or spontaneous bursts), responses exhibited a slow 15 msec rise to peak firing rates followed by a 35 msec decay. Interspike intervals within the response exhibited accelerandodecelerando patterns similar to those of spontaneous bursts. After tonic mode activity (i.e., single spikes), responses had a nearly instantaneous 1.5 msec rise-to-peak followed by a 40 msec decay, with large spike counts (5.2 spikes per stimulus) similar to those evoked in burst mode (6.2 spikes per stimulus). Interspike intervals were longer in tonic mode and exhibited a decelerando pattern. Initial evoked spikes, however, had shorter latencies and greater synchrony, contributing to the rapid onset of tonic population response. Shifts from quiescent (presumed burst mode) to tonic SA could be induced by either previous whisker deflections or iontophoretic application of NMDA; both manipulations effected appropriate shifts from burst to tonic response spike patterns. In awake animals, burst and tonic firing in RT, as in thalamocortical relay nuclei, may reflect sensory processing strategies appropriate for different behavioral and attentional states.
Key words: TRN; inhibition; T-type calcium current; whisker; burst; tonic; vigilance
Received Sep. 26, 2002;
revised Mar. 17, 2003;
accepted Apr. 7, 2003.
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