Power Spectral Density Analysis in Spindles Epochs in Healthy Children

Sleep spindles are important components of the N-REM stage-2 in the sleep electroencephalogram (EEG). They are oscillatory EEG activities of fusiform morphology in the range of 10–16 Hz [1], and a duration between 0.5 and 3 s. Spindles have been associated with cognitive skills and sleep-dependent memory consolidation. The aim of this study is to assess differences in the before (“pre”), during (“dur”) and after (“post”) spindle epochs by means of main power spectral bands delta (2–4 Hz), theta (4–8 Hz), alpha (8–12 Hz), beta (12–30 Hz), gamma (30–44 Hz), total (2–44 Hz) and sigma bands (12–16 Hz), calculated by the Welch periodogram, and by Fractal dimension (FD). The analysis was carried out on 7 healthy children (mean age = 8.90 ± 1.34 years) deprived of sleep on the day of the acquisition to enhance the deep sleep during the recording. For each EEG record (standard 10–20, 19 electrodes, sampling rate 512 Hz), two neurophysiologists labeled the start and the end points of the three sleep epochs. The results showed statistical differences between “dur” and both “pre” and “post” epochs in almost all channels (except O1 and O2) for all bands, except gamma. Furthermore, the values of FD were significantly different between “dur” and both “pre” and “post” epochs, for all channels. The FD values in “dur” epochs were smaller than in both “pre” and “post” ones, showing a lower EEG complexity during spindles, compared with the “pre” and “post” epochs. FD values in “post” epochs were found similar to those in “pre” periods. These differences could be useful to comprehend the spindles changes during sleep time. Moreover, these data could help on understanding the system generator of the spindles.