Mpa32i

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.

Simultaneous intracortical recordings in the upper layers of visual area V4 were performed using two epoxy-insulated tungsten microelectrodes (1–3 MΩ, shank diameter 125 μm FHC Inc., Bowdoin, ME, USA; 330 μm distance between shanks). The electrode signals were amplified 4000x (1000x) (monkey T: 4x by a wideband preamplifier MPA32I and 1000x by a PGA 64, 1-5000 Hz, both Multi Channel Systems GmbH, Germany; monkey B: same setup but gain factor 10 for preamplifier and 100 for PGA) and digitized with 25 kHz sampling rate and 12 bit (16 bit) ADC resolution. The reference electrode for monkey T was the recording chamber, a titanium cylinder of 25 mm diameter implanted into the bone and touching the dura. The electrode signals of monkey B were referenced to a low impedance electrode (< 0.1 MΩ), positioned on top of an epidural array (contacting the bone), placed above area V1. Before recordings, the pRF for each recording site was mapped manually as the minimal response field based on multi-unit- and LFP-responses, while the animals performed a fixation task. Both microelectrodes were placed such that the recorded neurons shared major parts of their pRFs. Locations and colors for the two stimuli within the overlapping pRFs were chosen such that they caused responses of different strength.

Supported by agarose gel (2% agarose-HGT, Nacalai Tesque) on the brain, a 64-channel silicon probe (Isomura64-4x-tet-lin-A64, with 16 tetrode-like arrangements on four shanks; NeuroNexus Technologies) was inserted vertically into the left DMS (A: +1.0, L: +2.3, DV: +3.7 mm from bregma), DLS (A: −1, L: 4.5, DV: 4.6 from bregma), or SNc (A: −5.5, L: 0.8 ~ 2.4, DV: 7.5 from bregma) using a micromanipulator (SM-15A, Narishige) on a stereotaxic frame (SR-10R-HT, Narishige). Multineuronal (multiple isolated single unit) recordings were performed during the conditioning task. The neuronal activity was amplified by two main amplifiers (32 channel: FA-32, Multi-Channel Systems; final gain, 2000; band-pass filter, 0.5 Hz to 10 kHz) through two 32-channel head-stage miniature preamplifiers (MPA 32I, Multi-Channel Systems; gain 10). The amplified signals were digitized at 20 kHz with two 32-channel hard-disk recorders (LX-120, TEAC).