Single-cell reconstruction of whole-brain efferent projections from mouse ventral posteromedial thalamus

The ventral posteromedial thalamic nucleus (VPM) relays orofacial somatosensory signals to the primary somatosensory cortex (SSp), yet its functional heterogeneity remains poorly defined at single-cell resolution. We combined fluorescence micro-optical sectioning tomography (fMOST) with single-neuron whole-brain reconstruction to map projections of vesicular glutamate transporter 2-positive (VGluT2⁺) excitatory neurons in the ventrolateral subdivision of VPM (vlVPM). Using 88 high-quality neurons with validated completeness, we identified pronounced structural heterogeneity and classified two clusters with distinct axonal profiles. Notably, we report two key findings that challenge the classical view: vlVPM neurons preferentially target superficial SSp layers (L1-3) rather than layer 4 (L4), and a multi-target subpopulation simultaneously innervates the motor cortex and basal ganglia via collaterals, establishing direct anatomical links to motor regulatory networks. These anatomical findings demonstrate that vlVPM establishes diverse projection pathways beyond canonical sensory relays, enabling direct structural crosstalk between sensory and motor circuits. This work provides a single-cell resolution framework for interpreting the anatomical basis of thalamic involvement in sensorimotor coordination.