Stroke and Motor Recovery are Associated with Regional and Age-Specific Changes in Periodic and Aperiodic Cortical Activity

Normal aging is associated with widespread changes in neuronal structure, function, and activity. The consequences of focal brain injury on global neuronal activity in aged individuals are poorly understood. Historically, stroke and aging have been associated with changes in narrow-band periodic neuronal activity, however 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. Abnormalities in aperiodic activity have been identified in psychiatric disorders and stroke, are associated with cognitive dysfunction in aging, and have been hypothesized to reflect changes in excitation/inhibition balance. Here we sought to further explore changes in both periodic and aperiodic cortical activity in neurotypical intact young and aged healthy individuals and individuals with stroke. 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 stroke outcomes using previously obtained tests of motor outcome (box and block) to average whole cortex spectral slopes within the stroke group. Consistent with prior work we found a significant flattening (decrease in exponent) of power spectral slope with normal aging. We also found that both aging and stroke were associated with fewer periodic peaks within the power spectrum. 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 aging). Using MRIs from stroke participants we investigated the lesion locations most associated with changes in slope. Interestingly deep lesions were observed to have the greatest influence on cortical spectral slope. Finally, slope in the stroke group was correlated with performance on a test of manual dexterity, however this correlation was much more significant in aged individuals. 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 and that the degree of these changes may be related to stroke outcomes.