Local field potential (LFP) recordings in freely‐moving rats

Rats were stereotaxically implanted in the S1Bf with bipolar electrodes (Enamelled copper wire, diameter 220 μm; Block, Verden, Germany) when they were anaesthetized with a mixture of xylazine (5‐10 mg kg⁻¹ i.p.; Rompun®; Centravet, Taden, France) and ketamine (40–100 mg kg⁻¹ i.p.; Clorketam1000®; Vetoquinol, Lure, France). Incisions and compression points were infiltrated with lidocaine (2%; Centravet). Stereotaxic co‐ordinates were antero‐posterior from bregma (AP): −2.5 mm; mediolateral: −5.5 mm; dorsoventral: −2.5 mm (Paxinos & Watson, 2007). A stainless steel screw (diameter 1 mm) inserted over the cerebellum served as the reference electrode. All electrodes were soldered to a female microconnector (BLR150Z; Fischer Elektronik, Lüdenscheid, Germany) and secured on the head of the animal with dental cement.

After a post‐surgery recovery period of 1 week, LFPs were acquired from freely‐moving rats with a digital acquisition system (Coherence 3NT; Deltamed, Le Bouscat, France) with a sampling rate of 1024 Hz and analogue bandpass filtering between 1 and 256 Hz, synchronized with the video. Rats were recorded for 60 min. The occurrence of cortical discharges on LFP recordings was always confirmed with respect to the video.

Spectral analysis of cortical discharges was performed using ImaGIN, an open source SPM toolbox for intracranial electroencephalograms (https://f-tract.eu/software/imagin) written in Matlab (The MathWorks, Natick, MA, USA) for Fast Fourier Transforms (FFT) of intracortical LFPs, as described previously (Pouyatos et al. 2016). To determine the functional link between SWDs and gamma oscillations, we quantified the cross‐frequency coupling by phase‐coupling analysis using Brainstorm (Tadel et al. 2011), which is freely available for download online under the GNU general public license (http://neuroimage.usc.edu/brainstorm).