Theta:gamma phase coupling and evoked gamma activity reflect the fidelity of mental templates during memory matching in visual perception.

Abstract

Top-down predictions of future events shaped by prior experience are an important control mechanism to allocate limited attentional resources more efficiently and are thought to be implemented as mental templates stored in memory. Increased evoked gamma activity and theta:gamma phase-phase coupling over parieto-occipital areas have previously been observed when mental templates meet matching visual stimuli. Here, we investigated how these signatures evolve during the formation of new mental templates and how they relate to the fidelity of such. Based on single-trial feedback, participants learned to classify target shapes as matching or mismatching with preceding cue sequences. In the end of the experiment, they were asked to freely reproduce targets as means of template fidelity. We observed fidelity-dependent increments of matching-related gamma phase locking and theta:gamma phase coupling in early visual areas around 100-200-ms poststimulus over time. Theta:gamma phase synchronization and evoked gamma activity might serve as complementary signatures of memory matching in visual perception; theta:gamma phase synchronization seemingly most important in early phases of learning and evoked gamma activity being essential for transition of mental templates into long-term memory.