Aperiodic neural excitation of the prefrontal cortex offsets age-related decrease in hippocampal theta activity for spatial memory maintenance

Currently, there is a critical gap in age-related electrophysiological changes in the human brain and how they are correlated with individual decline and maintenance of spatial cognitive function. To characterize these complex neurocognitive changes using direct intracranial recordings, we isolated periodic band power from the aperiodic spectral slope from iEEG power spectra of 69 presurgical epilepsy patients between 19 and 61 years of age while they performed a virtual spatial navigation task. We found a flattening of aperiodic spectral slope in the prefrontal cortex, but also observed a steepening in the hippocampus, suggestive of region-specific changes in excitatory/inhibitory balance across aging. The hippocampus showed pronounced changes in periodic (oscillatory) activity, including a decrease in theta power that correlated with impaired spatial memory, potentially due to changes in the cholinergic system. Interestingly, individuals with the flatter spectral slope in DLPFC showed preserved performance despite lower hippocampal theta, indicating a potential compensatory mechanism for cognitive maintenance. These findings provide new evidence that individual age-related cognitive decline can be predicted by changes in hippocampal theta oscillation, in combination with concomitant prefrontal compensatory mechanisms.