Frequency and dependence of long range temporal correlations in human hippocampal energy fluctuations

Spontaneous energy fluctuations in human hippocampal EEG show prominent amplitude and temporal variability. Here we show hippocampal energy fluctuations often exhibit long-range temporal correlations with power-law scaling. In most cases this scaling behavior persisted on time scales in excess of 10 minutes, the maximum duration we could detect with our recording durations. During these epochs we find that the energy fluctuations exhibit long-range correlations over a broad frequency range (0.5-100 Hz) with greater persistence of the correlations in the lower frequency bands (0.5-30 Hz) than the higher (30-100 Hz). The correlation in hippocampal energy fluctuations is characterized by a bias for energy fluctuations to be followed by similar magnitude fluctuations over all energy scales, i.e. large fluctuations begets large fluctuations and small begets small.