Animal procedures

All experiments were performed in accordance with the French Ethical Committee (Direction générale de la recherche et de l’innovation) and European legislation (2010/63/EU). Procedures were approved by the French Ministry of Education in Research after consultation with the ethical committee #59 (authorization number 2015060516116339). The recordings were performed in three male Wistar rats (260 ± 16 g). The rats were first anesthetized with 3% isoflurane that was mixed with 80% N₂O and 20% O₂ and delivered at 1 liter/min. Once deeply anesthetized, animals were placed into a stereotactic device with ear bars and a nose clamp. The body temperature was monitored with a rectal probe and maintained at 37°C. The eyes were coated with an ophtalmic gel (Opthalon) to keep them from drying out. Lidocaine (1%) was injected below the skin 10 min before a straight incision was made along the sagittal suture of the skull. The incision was stretched and held with surgical clamps. The bone was cleaned, and a head fixation post was cemented to the right parietal bone. A small craniotomy (~0.5 mm) was then made over the left frontal lobe, and a small electrocorticography (ECoG) electrode was placed under the skull in contact with the surface of the brain. Through this electrode, the depth of the anesthesia was continually assessed throughout the experiment. A second craniotomy was performed over the barrel cortex (~5.7 mm lateral and 3.7 mm posterior to bregma) that was ~2 mm in diameter. After performing a durotomy, a four-shank (or single-shank) silicon probe was inserted at an angle of 58° with respect to the surface of the brain to a depth of ~1.4 to 1.5 mm. Once the electrode was in position, the anesthesia was lightened by gradually decreasing the isoflurane concentration until the ECoG was stable in stage III, plane 1 to 2. Throughout the experiment, the physiological state of the animal was controlled such that the respiration rate stayed in the range of 1 to 1.5 Hz, there was a lack of motor activity in both the paws and the eyes, and the ECoG showed fast oscillations (>5 Hz), as has been shown to maintain functional responses in the cortex (12).