Nichrome wire

After rats trained to perform the CC and the IC tasks, they were anesthetized with pentobarbital sodium (50 mg/kg, i.p.) and placed in a stereotaxic frame. The skull was exposed and holes were drilled in the skull over the recording site. Four drivable electrode bundles were implanted and fixed in the DMS in the left hemisphere (1.0 mm posterior, 1.6 mm lateral from bregma, 3.7 mm ventral from the brain surface), the DLS in the right hemisphere (1.0 mm anterior, 3.5 mm lateral from bregma, 3.3 mm ventral from the brain surface), the mPFC in the left hemisphere (3.2 mm anterior, 0.7 mm lateral from bregma, 2.0 mm ventral from the brain surface), and the M1 in the right hemisphere (1.0 mm anterior, 2.6 mm lateral from bregma, 0.4 mm ventral from the brain surface) using pink dental cement with confirmed effects on the brain (Yoshizawa and Funahashi, 2020 (link)).
An electrode bundle was composed of eight Formvar-insulated, 25-μm bare diameter nichrome wires (A-M Systems) and was inserted into a stainless-steel guide cannula (0.3 mm in outer diameter; Unique Medical). Tips of the microwires were cut with sharp surgical scissors so that ∼1.5 mm of each tip protruded from the cannula. Each tip was electroplated with gold to obtain an impedance of 100–200 kΩ at 1 kHz. Electrode bundles were advanced by 125 μm per recording day to acquire activity from new neurons.

Animals were premedicated with diazepam (2–5 mg/kg; i.p.), glycopyrrolate (0.05 mg/kg; s.c.), carprofen (5 mg/kg; s.c.), and butorphanol tartrate (0.5 mg/kg; s.c.) to counteract respiratory effects of anesthesia, to control pain, and to decrease risk of seizures. They were brought to a surgical level of anesthesia with isofluorane (1.0%–2.5%). Using a stereotaxic apparatus (Kopf, Tujunga, CA), rats were unilaterally implanted with a custom hyperdrive into the pulvinar at −3.9 mm AP, ± 1.8 mm ML, and −4.0 mm DV relative to bregma. Three rats were targeted in the left pulvinar; two rats were targeted in the right pulvinar. The hyperdrive had fifteen microdrives, each consisting of a drivable screw with guide tubing containing one stereotrode. Five microdrives of each hyperdrive were implanted in the pulvinar. Stereotrodes were made of two 12 μm twisted, formvar-insulated nichrome wires (A-M systems, Sequim, WA, USA). A full turn of the screw advanced the stereotrode by 350 μm. Two silver ground wires were wrapped around anchor screws in the skull. The hyperdrive was secured to the skull by the ground screws, small anchor screws, grip cement (Dentsply Caulk, Milford, DE, USA), and dental cement (Coltene/Whaledent Inc., Cuyahoga Falls, OH, USA).