The impact of 'bursting' thalamic impulses at a neocortical synapse

Abstract

Considerable effort has gone into understanding the mechanisms underlying high-frequency 'bursting' of thalamocortical impulses, their sensory information content and their involvement in perception. However, little is known about the influence of such impulses on their cortical targets. Here we follow bursting thalamic impulses to their terminus at the thalamocortical synapse of the awake rabbit, and examine their influence on a class of somatosensory cortical neurons. We show that thalamic bursts potently activate cortical circuits. Initial impulses of each burst have a greatly enhanced ability to elicit cortical action potentials, and later impulses in the burst further raise the probability of eliciting spikes. In some cases, multiple cortical spikes result from a single burst. Moreover, we show that the interval preceding each burst is crucial for generating the enhanced cortical response. The powerful activation of neocortex by thalamocortical bursts is fully consistent with an involvement of these impulses in perceptual/attentional processes.

A Behavioral Role for Feature Detection by Sensory Bursts

“…For bat-evasion responses, however, isolated AN2 spikes may simply be "noise," which is filtered out by the fact that only bursts elicit strong behavioral responses. Noise filtering by bursts has been shown in other systems in which, because of synaptic summation or facilitation, bursts are particularly effective in driving their target cells (Boyan and Fullard, 1988;Lisman, 1997;Swadlow and Gusev, 2001). The same may be true of the interactions of AN2 with its target neurons.…”

Long-range projections coordinate distributed brain-wide neural activity with a specific spatiotemporal profile

“…However, recent evidence suggests that thalamic bursting plays a fundamental role in sensory processing (53,54). Studies of visual (55) and somatosensory (30,53) pathways demonstrate the presence of thalamic bursting in awake and attentive states, implying that bursting activity modulates sensory perception.…”

“…However, recent evidence suggests that thalamic bursting plays a fundamental role in sensory processing (53,54). Studies of visual (55) and somatosensory (30,53) pathways demonstrate the presence of thalamic bursting in awake and attentive states, implying that bursting activity modulates sensory perception. Intermittent activation of multiple long-range circuits to integrate major sensory cortices suggests that multisensory integration is essential to shape sensory perceptions that could not otherwise be achieved with only one sense (56,57).…”

Higher-order thalamic relays burst more than first-order relays

“…This firing mode strongly affects the nature of the signal that is relayed to the cortex (4). For example, compared with tonic mode, burst mode produces much more nonlinear distortion in the relay of information, but the information relayed has greater detectability because of a greater signal-to-noise ratio and stronger activation of postsynaptic cortical targets (4)(5)(6)(7)(8)(9). From these properties, the hypothesis has been forwarded that burst firing, with its greater detectability and cortical activation, serves as a ''wake-up call'' to the cortex that there has been a change in the outside world (e.g., a novel stimulus within the receptive field of a relay cell for one of the sensory thalamic nuclei); tonic mode, with its more linear relay of information, is then better suited for a more faithful analysis of the relayed information (4,7).…”