Early, partly anticipatory, neural oscillations during identification set the stage for priming

Perceptual priming is a fundamental long-term memory capability by which exposure to a stimulus improves later perceptual processing of that stimulus. A widespread hypothesis is that priming is the later result of perceptual learning during stimulus identification. Testing this hypothesis involves isolating priming without explicit memory, and appropriately measuring brain activity during initial experimental exposure to assess whether brain activity related to identification differs as a function of later priming. Here, we show, using magnetoencephalography (MEG), that words primed in a later test are distinguished from unprimed words at initial exposure by (a) more specific responses in perceptual brain areas, indicated by an early (within 240 ms after word onset) decrease in amplitude but increase in phase alignment of beta and gamma oscillations, and (b) improved coordination of responses across perceptual and higher brain areas in the same time window, indicated by an increase in interareal phase synchrony of alpha oscillations. The increase in interareal phase synchrony partly started already in the pre-stimulus period, approximately 60-80 ms prior to word onset, showing that the improved coordination of responses across areas was partly anticipatory. The anatomy and early timing of these patterns reveal a neural link between identification and long-term memory. The pre-stimulus findings additionally show that priming is related to the stimulus-specific anticipatory state of visual identification areas at initial exposure.