Cross-frequency phase synchronization: a brain mechanism of memory matching and attention.

Spatial attention amplifies the neural response, i.e. spike rates, brain metabolism, and oscillatory activity at gamma frequency (beyond 30 Hz). In this study we show that when a visual target is attended enhanced synchrony between gamma phase (30 to 50 Hz) and theta phase (4 to 7 Hz), representing bottom-up and top-down activity, respectively, can be observed. This is interpreted as memory matching between incoming visual information and stored (top-down) information. The results highlight the function of oscillatory brain activity in the integration of memory and attention processes. This seems to be true in particular for theta oscillations showing increased interregional phase-coupling. We conclude that memory information is stored within a distributed theta network and it is matched with an incoming sensory trace at posterior brain areas.