Cell Type–Specific Three-Dimensional Structure of Thalamocortical Circuits in a Column of Rat Vibrissal Cortex

TLDR

Soma location, dendrite morphology, and synaptic innervation are key determinants of individual neuron functional responses, such as sensory‑evoked spiking. The study reconstructs the 3D circuits of lemniscal thalamocortical afferents and excitatory neurons in a defined cortical column of rat vibrissal cortex. The authors objectively classified nine cortical cell types and quantified the distribution of their somata, dendrites, and thalamocortical synapses. The data show that while somata and dendrites of most cell types intermingle, thalamocortical connectivity is strongly cell‑type– and soma‑location dependent, and that lemniscal afferents explain layer‑specific subthreshold and spiking responses after passive whisker touch, providing a quantitative 3D wiring diagram that links structure to function at single‑cell resolution.

Abstract

Soma location, dendrite morphology, and synaptic innervation may represent key determinants of functional responses of individual neurons, such as sensory-evoked spiking. Here, we reconstruct the 3D circuits formed by thalamocortical afferents from the lemniscal pathway and excitatory neurons of an anatomically defined cortical column in rat vibrissal cortex. We objectively classify 9 cortical cell types and estimate the number and distribution of their somata, dendrites, and thalamocortical synapses. Somata and dendrites of most cell types intermingle, while thalamocortical connectivity depends strongly upon the cell type and the 3D soma location of the postsynaptic neuron. Correlating dendrite morphology and thalamocortical connectivity to functional responses revealed that the lemniscal afferents can account for some of the cell type- and location-specific subthreshold and spiking responses after passive whisker touch (e.g., in layer 4, but not for other cell types, e.g., in layer 5). Our data provides a quantitative 3D prediction of the cell type–specific lemniscal synaptic wiring diagram and elucidates structure–function relationships of this physiologically relevant pathway at single-cell resolution.