Multi spike detector

After training completion, a head-restraint system and a recording chamber were surgically implanted in asepsis and under general anesthesia (sodium thiopental, 8 mg/kg/h, i.v.) following the procedures reported in Galletti et al. (1995) (link). Adequate measures were taken to minimize pain or discomfort. A full program of postoperative analgesia (ketorolac trometazyn, 1 mg/kg, i.m., immediately after surgery, and 1.6 mg/kg, i.m., on the following days) and antibiotic care [Ritardomicina® (benzathine benzylpenicillin + dihydrostreptomycin + streptomycin) 1–1.5 ml/10 kg every 5–6 d] followed the surgery.
Single-cell activity was extracellularly recorded from areas V6A, PEc, and PE of the two monkeys (Fig. 1). We performed single microelectrode penetrations using a 5-channel multielectrode recording system (MiniMatrix, Thomas Recording, GmbH). The electrode signals were amplified (at a gain of 10,000) and bandpass filtered (between 0.5 and 5 kHz). Action potentials in each channel were isolated online with a waveform discriminator (Multi Spike Detector; Alpha Omega Engineering). Spikes were sampled at 100 kHz. The present study includes neurons assigned to areas V6A, PEc, and PE following the cytoarchitectonic criteria of Pandya and Seltzer (1982) (link) and Luppino et al. (2005) (link).

For technical reasons, we recorded neuronal activity in the monkey positioned to the left of the other one. Single-neuron activity in the LPFC was recorded extracellularly using tungsten electrodes (2.0–8.0 MΩ, FHC, Bowdoinham, ME). An electrode was advanced with a hydraulic microdrive (MO-95C, Narishige, Tokyo, Japan) through a stainless steel guide tube. Neuronal activities were converted into pulses using a spike waveform detector (Multispike Detector, Alpha Omega Engineering, Nazareth, Israel). We recorded activity in the right hemisphere of monkey S and in both hemispheres of monkey H while they were playing the games. Monkey P was always the competitor for monkeys H and S, which never competed against each other because both of them were trained with the same turret color (white). The recording area covered both the dorsal and ventral banks of the principal sulcus (Figure 8A), and was determined in reference to magnetic resonance images (whole-brain coverage, slice thickness 2 mm, Siemens, Sonata 1.5T).
We monitored the eye position of monkeys H and S with an infrared eye-camera system (sampling rate, 4 ms; R-22C-1, ISEYO Electronic, Tokyo, Japan), but did not restrict or control their eye movements.

The position of each monkey’s gaze was recorded with an infrared oculometer (Bouis Instrument, Karlsruhe, Germany). Single-unit potentials were isolated using a 16-electrode microdrive with independent control of each electrode (Thomas recording, Giessen, Germany) through a custom, concentric recording head with 518 µm electrode spacing. The signal from each quartz-insulated platinum-iridium electrode (impedance, 0.5–1.5 MΩ at 1 kHz) was amplified and discriminated using a Multispike Detector (Alpha-Omega Engineering, Nazareth, Israel) or a Multichannel Acquisition Processor (Plexon, Dallas, TX). For the latter, we resorted neuronal waveforms with Offline Sorter (Plexon). NIMH CORTEX software (https://www.nimh.nih.gov/labs-at-nimh/research-areas/clinics-and-labs/ln/shn/software-projects.shtml) controlled behavior and collect data.