Figure 1.
Data overview and spindle detection. A, Illustration of flexible probes used for simultaneous recording of depth EEG (platinum contacts, blue) and unit activity (microwires, green). B, Overview of 129 depth electrode locations in 13 individuals spanning multiple brain regions as seen from medial view. SM, Supplementary motor; PC/P, posterior cingulate/parietal cortex; PH, parahippocampal gyrus; HC, hippocampus; E, entorhinal cortex; Am, amygdala; LH, left hemisphere; RH, right hemisphere. C, Example power spectra of scalp EEG in one representative individual in stage N2 sleep (blue), N3 sleep (red), and REM sleep (green). Note high power in slow-wave (<4 Hz) and spindle (9–16 Hz) range in NREM sleep. D, Hypnogram: time course of sleep–wake stages in the same individual. W, Wake; R, REM sleep; N1–N3, NREM sleep, stages 1–3. E, Spindle detection step 1: channels with spindle activity in NREM sleep are chosen for further analysis. Spectral profiles of a typical selected channel (parietal lobe, top) and a typical discarded channel (amygdala, bottom). For each channel, power in NREM sleep (red) was compared with a 1/fα model (blue), and channels with a significant peak (asterisks) in the range of 9–16 Hz are considered for further analysis. Yellow dots denote frequency with maximal power difference and error bars denote SEM across 10 s epochs of NREM sleep. F, Spindle detection step 2: individual spindles were selected based on their power and duration. Raw EEG (top row) is filtered in the spindle range (9–16 Hz, second row). The instantaneous amplitude is extracted via the Hilbert transform (red trace, third row). A detection threshold is set at mean + 3 SD of spindle power across NREM sleep (horizontal black line, fourth row) and peaks exceeding this threshold (red dot) are considered putative spindles. A start/end threshold is set at mean + 1 SD of spindle power across NREM sleep (horizontal green line, bottom row), thereby defining start and end times (cyan and green dots, respectively) and determining spindle duration (between 0.5 and 2 s). G, Spindle detection step 3: channels in which power increases of detected events were specific to the spindle range rather than broadband were chosen for final analysis. Spectral profiles of detected events in a typical selected channel (parietal lobe, top) and a typical discarded channel (entorhinal cortex, bottom). For each channel, power of detected events (red) is compared with power of random 1 s segments (blue), and channels with a significant peak which is specific to the spindle range (9–16 Hz) are chosen for final analysis. Note that detected events in entorhinal cortex had a diffuse broadband power increase. Yellow dots and error bars as above.