Objective: Sleep spindles (12-15 Hz oscillations) are one of the hallmarks of the electroencephalogram (EEG) during human non-rapid eye movement (non-REM) sleep. The effect of a 40 h sleep deprivation (SD) on spindle characteristics along the antero-posterior axis was investigated.
Methods: EEGs during non-REM sleep in healthy young volunteers were analyzed with a new method for instantaneous spectral analysis, based on the fast time frequency transform (FTFT), which yields high-resolution spindle parameters in the combined time and frequency domain.
Results: FTFT revealed that after SD, mean spindle amplitude was enhanced, while spindle density was reduced. The reduction in spindle density was most prominent in the frontal derivation (Fz), while spindle amplitude was increased in all derivations except in Fz. Mean spindle frequency and its variability within a spindle were reduced after SD. When analyzed per 0.25 Hz frequency bin, amplitude was increased in the lower spindle frequency range (12-13.75 Hz), whereas density was reduced in the high spindle frequency range (13.5-14.75 Hz).
Conclusions: The observed reduction in spindle density after SD confirms the inverse homeostatic relationship between sleep spindles and slow waves whereas the increase in spindle amplitude and the reduction in intra-spindle frequency variability support the hypothesis of a higher level of synchronization in thalamocortical cells when homeostatic sleep pressure is enhanced.