A topographic axis of transcriptional identity across thalamic projection systems

Thalamus is the central hub for forebrain communication, a function mediated by approximately 30 nuclei. To uncover organizational principles of the thalamic pathways providing input to the forebrain, we produced a near-comprehensive transcriptomic atlas of its major projection classes. We found that almost all nuclei belong to one of three major profiles that lie on a single axis of variance aligned with the mediolateral axis of thalamus. This axis of variance is strongly enriched in genes encoding receptors and ion channels, and we show that each profile exhibits different electrophysiological signatures. Single-cell profiling revealed even further heterogeneity within established nuclear boundaries, suggesting that the same input to a given nucleus might be differentially processed. Together, our analysis shows striking covariation in the organization of thalamic pathways serving all input modalities and output targets, establishing a simple and comprehensive thalamic functional architecture.