Dynamic relationships between sleep spindles and delta waves during a NREM period

All-night sleep EEGs from 7 normal young male adults were analyzed by a waveform recognition method using FFT-IFFT band pass filters. The total durations of sleep spindles and sleep delta waves in each 20-s epoch were measured and plotted on an X-Y graph with lines connecting the points in time sequence (dynamic two-component plot). The relationship between these two measures within a single NREM period showed three dynamic phases and one stationary period. In the first phase, spindles increased while delta remained at a low level or increased slightly. In the second phase, delta increased greatly while spindles decreased. In the third phase, delta decreased while spindles remained at a low level. There was a stationary period between the second and third phases, when delta maintained a higher level and spindles maintained a lower level. These dynamic descriptions reflect the underlying physiological mechanisms more directly than static sleep stages. They should also permit finer analyses of sleep in psychiatric and neurological disorders.