Alpha power analysis focused on the mean spectral power from 8–14 Hz, 100–400 ms post-target onset, collapsed across occipital and parietooccipital electrodes on memory blocks. We used two-tailed t-tests to compare power values across age groups and stimulation conditions. We confirmed the results of this hypothesis-driven approach with a hypothesis-independent approach that makes no a priori assumptions about the precise spectral or temporal nature of the effect. For this analysis, power was averaged across occipital and parietooccipital electrodes, and assessed from 0 to 500 ms post-target onset in 10-ms increments for each frequency from 2 to 30 Hz in 1-Hz increments. Two-tailed t-tests were computed between age groups and stimulation conditions and a false discovery rate (FDR) was set to α = 0.01 to control for multiple comparisons 95. Results showed significantly (pcorrected < 0.01) greater alpha power reduction in younger relative to older adults in the sham condition from 130–360 ms and 9–11 Hz, and younger adults in the sham condition relative to older adults in the active condition from 140–300 ms and 10–12 Hz, but no modulations in older adults between sham and active conditions reached significance.
