Thalamic state influences timing and feature selectivity in the thalamocortical circuit

Thalamic neurons dynamically encode sensory information in a state-dependent manner as a mechanism for gating information flow to the cortex. Here, we investigated the role of thalamic state on precise feature selectivity in the thalamocortical circuit of the rat vibrissa pathway. In thalamic neurons, tonic spike triggered averaging revealed clear feature selectivity, while the feature selectivity associated with burst spikes could not be recovered with this approach. These thalamic state dependent changes propagated to cortex such that the cortical feature selectivity was diminished during the optogenetically hyperpolarized (burst biased) thalamic condition. Further analysis revealed that the perceived loss of feature selectivity was likely not due to a true loss of stimulus selectivity but instead to changes in the precision of the temporal spiking in burst firing modes. Therefore, alterations to thalamic state enable a dynamic interplay between spike timing and spike rate that shapes stimulus encoding in the thalamocortical circuit.