Stroke and motor outcomes are associated with regional and age-specific changes in periodic and aperiodic cortical activity

Historically, stroke and ageing have been associated with changes in narrow-band periodic neuronal activity, but recent work has highlighted the importance of broad-band aperiodic activity. Aperiodic activity is represented by the 1/f slope of power spectral density generated by cortical activity. Here we explored changes in both periodic and aperiodic cortical activity in neurologically intact individuals and individuals with stroke, across the lifespan. We compared ‘resting state’ electroencephalograms from all participants after applying the specparam algorithm, which decomposes the power spectrum into aperiodic and periodic components. We also correlated motor outcomes to average whole cortex spectral slopes within the stroke group. We found a significant flattening (decrease in exponent) of power spectral slope with normal ageing. We found that both ageing and stroke were associated with fewer periodic peaks. Interestingly, we found that stroke was associated with a significant increase in spectral slope, but age moderated this effect. Younger stroke patients showed minimal difference in slope while older stroke patients had significantly steeper slopes (opposite to the direction in normal ageing). We next investigated the lesion locations most associated with changes in slope. Deep lesions were observed to have the greatest influence on cortical spectral slope. Finally, the slope in the stroke group was associated with performance on a test of manual dexterity, but this association was stronger in older individuals, and varied by scalp region. Our data suggest that stroke in the aged brain has unique effects on aperiodic activity possibly reflecting unique influence of injury on cerebral excitation/inhibition balance in aged individuals.