To examine block (memory, control) x age group (young, old), and block (memory, control) x stimulation (sham, active) interactions on memory-specific PAC, we performed linear regression using regressors representing these interactions, allowing us to assess PAC across the full frequency spectrum of the analysis. We used cluster permutation statistics corrected for multiple comparisons to test for significance. Neighboring phase and amplitude frequencies that fell below a p-value of 0.05 were grouped into clusters. A null distribution was created with permutated data across subjects (1000 permutations). To do this, we performed an identical analysis to that described above, except instead of using the actual regressor of block and age group, or block and stimulation condition, we randomly shuffled the values in those regressors. For example, we randomly assigned data to memory block versus control block and sham versus active conditions. We calculated the maximum cluster-level test statistic, providing a corrected p-value for each cluster. Clusters with a pcorrected < 0.01 were considered significant.
