Aperiodicity in mouse CA1 and DG power spectra

Rodent hippocampal power spectra comprise of periodic and aperiodic components. The periodic components (brain rhythms) contain information about the behavioral or cognitive state of the animal. The aperiodic components are rarely studied and their functionality is not well understood, though have shown to be correlated with animals age or the excitation-inhibition ratio of the brain region. To study these components in the mouse hippocampus we modified the existing open-source FOOOF toolbox, which was originally optimized for EEG data. First, using simulated data, we show that our modifications decrease the error in assessment of the periodic components from 3% to 0.1%. Second, using tetrode electrophysiological signals, we compare the aperiodic activity within mice hippocampal sub-regions, CA1 and dentate gyrus (DG). Our optimization of FOOOF improved the aperiodic assessment errors by about 50% and were critical in making the first-ever assessments of the aperiodic components in these brain regions. Our results show that the aperiodic parameters in the DG are multi-fold and significantly larger than in CA1, revealing higher excitation and longer timescales in CA1 than DG. Our work highlights the subtle differences in electrophysiology field potentials between hippocampal sub-regions, and presents the improvements needed in the existing open-source toolbox to be able to see such differences.