Sm 15

We performed extracellular multi-neuronal (multiple, isolated, single-unit) recordings from individual neurons while the rats were performing behavioral tasks. A supportive layer of agarose gel (2% agarose-HGT, Nacalai Tesque, Kyoto, Japan) was placed on the brain, and then 32-channel silicon probes (Iso_3x_tet-A32 or Iso_4x_tet-A32; NeuroNexus Technologies, Ann Arbor, MI, USA) were precisely inserted into CA1 and the LEC. Insertions were performed using fine micromanipulators (SM-15 or SMM-200B, Narishige) at least 1 h before the start of each recording experiment.
Wide-band signals were amplified and filtered (FA64I, Multi Channel Systems, Reutlingen, Germany; final gain, 2000; band-pass filter, 0.5 Hz to 10 kHz) through a 32-channel head stage (MPA32I, Multi Channel Systems; gain, 10). These signals were digitized at 20 kHz and recorded with three 32-channel hard-disc recorders (LX-120, TEAC, Tokyo, Japan) that simultaneously digitized the pedal positions tracked by angle encoders and the events resulting from optogenetic stimulation.

This experiment was approved by the Committee on Animal Care Use and by the Ethical Committee of the National Institute of Advanced Industrial Science and Technology. Male Wistar rats (325 ± 25 g; SLC Inc., Tokyo, Japan) were used in all experiments (n = 7). The animals were group housed in a standard cage under a 12 h light/dark cycle with food and water provided ad libitum. The rats were anesthetized with isoflurane (3.0% induction, 1.50%–1.25% maintenance) and fixed in a stereotaxic frame for the experiments. A craniotomy was performed to create a circular cranial window (3.5 mm in diameter) over the secondary motor cortex (M2; anteroposterior, 3.0 mm; mediolateral, 1.0 mm from the bregma [22 ]). After removing the dura in the cranial window, the tube-shaped implantable device was carefully placed on the exposed cortex using a micro manipulator (SM-15, Narishige, Tokyo, Japan) and fixed to the skull surface using silicon adhesive (for packing) and dental acrylic cement (for fixing). After the surgery, the tube was filled with ACSF (124 mM NaCl, 2.5 mM KCl, 2 mM CaCl₂, 2 mM MgSO₄, 1.25 mM NaH₂PO₄, 26 mM NaHCO₃, and 10 mM glucose) and sealed with silicon adhesive (Kwik-Sil; WPI, Sarasota, FL, USA).