PT - JOURNAL ARTICLE AU - Naoki Yamawaki AU - Martinna G. Raineri Tapies AU - Austin M. Stults AU - Gregory A. Smith AU - Gordon M. G. Shepherd TI - Circuit organization of the excitatory sensorimotor loop through hand/forelimb S1 and M1 AID - 10.1101/2021.01.22.427843 DP - 2021 Jan 01 TA - bioRxiv PG - 2021.01.22.427843 4099 - http://biorxiv.org/content/early/2021/01/24/2021.01.22.427843.short 4100 - http://biorxiv.org/content/early/2021/01/24/2021.01.22.427843.full AB - Sensory-guided limb control relies on communication across sensorimotor loops. For active touch with the hand, the longest loop is the transcortical continuation of ascending pathways, particularly the lemnisco-cortical and corticocortical pathways carrying tactile signals via the cuneate nucleus, ventral posterior lateral (VPL) thalamus, and primary somatosensory (S1) and motor (M1) cortices to reach corticospinal neurons and influence descending activity. We characterized excitatory connectivity along this pathway in the mouse. In the lemnisco-cortical leg, disynaptic cuneate→VPL→S1 connections excited mainly layer (L) 4 neurons. In the corticocortical leg, S1→M1 connections from L2/3 and L5A neurons mainly excited downstream L2/3 neurons, which excite corticospinal neurons. The findings provide a detailed new wiring diagram for the hand/forelimb-related transcortical circuit, delineating a basic but complex set of cell-type-specific feedforward excitatory connections that selectively and extensively engage diverse intratelencephalic projection neurons, thereby polysynaptically linking subcortical somatosensory input to cortical motor output to spinal cord.Competing Interest StatementThe authors have declared no competing interest.