Further evidence that phase-amplitude CFC may play a functional role in cortical processing comes from a study by Axmacher and colleagues [53]. Recording from multiple hippocampal sites in humans, Axmacher et al showed that the frequency for phase in phase-amplitude CFC depends on working memory load, with higher working memory load corresponding to a lower frequency for phase. That is, while the phase frequency remained within the theta range throughout the working memory task, a load of one item corresponded to a CFC peak at the upper end of the frequency range while a load of four items corresponded to a CFC peak at the lower end of the theta frequency range (Figure 1E–G).
