Dii lipophilic carbocyanine dye

Animals were anesthetized with urethane (1 g/kg) and mounted on the stereotaxic frame (Fig. 4); supplementary doses (0.15 g/kg) were given during the recording when necessary. Silicon probe–based recordings were performed through a craniotomy (1.4 mm by 2.5 mm) centered at 0.6 mm anterior and 3.7 mm lateral to bregma. All the stereotaxic coordinates were selected on the basis of previous reports focused on the DLS forelimb region (8 (link)). Histological confirmation of silicon probe position in the brain was achieved by applying DiI lipophilic carbocyanine dye (1%; Sigma-Aldrich) to the back of the probes before insertion. For optogenetic experiments, an optical fiber (200 mm) was directed to M2 (coordinates: AP, 3.5; ML, 1.9; DV, 1.3) or S1 (coordinates: AP, 0.6; ML, 3.6; DV, 1.3), contralaterally to the recording site. The silicon probe was slowly lowered to record neuronal activity from the S1 forelimb region (0.8- to 1.6-mm depth) and until the DLS (3.5- to 4.5-mm depth). For each animal, we performed recordings in 2 to 3 and 3 to 5 depths (at least 250 μm between each depth) in the S1 and DLS, respectively. Immediately after the experiments, animals were injected with a lethal dose of pentobarbital and transcardially perfused. The brains were extracted and processed for histology.