Convergence of Cortical and Sensory Driver Inputs on Single Thalamocortical Cells

TLDR

Thalamus relays ascending and descending information via strong driver pathways that are organized in parallel streams and do not interact at the thalamic level. The study investigates whether driver inputs from different sources can interact at single thalamocortical cells in the rodent somatosensory thalamus. The authors used electron microscopy, optogenetics, and in vivo physiology to examine this interaction. Anatomical and physiological data show that ascending brainstem and descending cortical layer 5 inputs converge and synergistically interact on single POm thalamocortical neurons, producing supralinear output that encodes the relative timing of sensory events and cortical activity, demonstrating that these neurons integrate raw sensory information with cortical signals and relay the integrated activity back to cortex.

Abstract

Ascending and descending information is relayed through the thalamus via strong, "driver" pathways. According to our current knowledge, different driver pathways are organized in parallel streams and do not interact at the thalamic level. Using an electron microscopic approach combined with optogenetics and in vivo physiology, we examined whether driver inputs arising from different sources can interact at single thalamocortical cells in the rodent somatosensory thalamus (nucleus posterior, POm). Both the anatomical and the physiological data demonstrated that ascending driver inputs from the brainstem and descending driver inputs from cortical layer 5 pyramidal neurons converge and interact on single thalamocortical neurons in POm. Both individual pathways displayed driver properties, but they interacted synergistically in a time-dependent manner and when co-activated, supralinearly increased the output of thalamus. As a consequence, thalamocortical neurons reported the relative timing between sensory events and ongoing cortical activity. We conclude that thalamocortical neurons can receive 2 powerful inputs of different origin, rather than only a single one as previously suggested. This allows thalamocortical neurons to integrate raw sensory information with powerful cortical signals and transfer the integrated activity back to cortical networks.