Electrophysiological data recording a preprocessing
ANT and MD LFP, and all-night sleep EEG signals were recorded by SD-LTM 64 Express EEG/polygraphic recording system. Physiological signals were recorded at 8192 Hz/channel effective sampling rate with 22 bit precision and hardware input filters set at 0.02 (high pass: 40 dB/decade) and 450 Hz (low pass: 40 dB/decade). Data was decimated by a factor of 4 by the firmware resulting in stored time series digitized at 2048 Hz/channel. LFP signals were assessed by bilateral (L – left, R – right) quadripolar electrodes applying bipolar reference scheme and focusing only on those leads which were derived from two adjacent contacts positioned in the same thalamic nucleus or alternatively from the BRIDGE area (bipolar recordings with one contact within the ANT and the second contact in adjacent tissue Deutschová et al. 2021). The number of ANT and MD derivations recorded for each patient is reported in Table 2. Scalp EEG was recorded according to the international 10-20 system (Fp1, Fp2, Fpz, F3, F4, F7, F8, C3, C4, T3, T4, T5, T6, P3, P4, O1, O2, Oz; Jasper 1958) extended with the inferior temporal chain (F9, F10, T9, T10, P9, P10) and two anterior zygomatic electrodes (ZA1, ZA2; Manzano et al. 1986), with the reference placed at the CP1 and ground placed at CP2 locations. Submental electromyograms (EMGs) were recorded by bipolarly referenced electrodes placed on the chin. For two patients (#1 and #2) the EEG electrode set up were slightly different from the above described montage. For patient #1 no Fpz, P9, P10 and EMG time series were recorded, and for patient #2 F3, F4, C3, C4, P3 and P4 electrodes were missing, although the electrode position at Pz was present in this patient. Data from missing electrodes were treated as missing values in further analyses.
Continuous EEG and LFP recordings were automatically segmented into 90 minutes chunks by the recording software. During the recording session there were no explicit light off and light on time, thus, the first and the last chunk for data analysis were selected as follows: a 90 minutes segment were required to contain at least 10 minutes of continuous sleep in the second or in the first halves, respectively for the first and last chunks. EEG data were offline re-referenced to the mathematically-linked T9 and T10 electrodes. All-night sleep records were scored for sleep-waking states and stages according to standard AASM criteria on 20 seconds basis (Berry et al. 2015) by an expert. Furthermore, artefactual segments were marked on 4 seconds basis and excluded from quantitative EEG and time series analyses.