Studies which assess long-range theta synchronization reveal increased connectivity during successful memory, even in relatively nonspecific memory success contrasts. One possible explanation is that while averaging across electrodes washes out local increases in power, it retains inter-regional connectivity. Alternatively, decreases in power could be mechanistically related to increases in inter-regional synchrony -- further research is necessary to distinguish between these possibilities (see Outstanding Questions). Relatedly, the fact that scalp EEG measures both changes in local power and changes in synchrony between nearby areas could explain some of the discrepancies between invasive and non-invasive studies. Scalp EEG studies may more reliably report increases in theta power associated with good memory because power measured at the scalp reflects large-scale neural synchrony, even as local theta amplitude is diminished.
