Involvement of the parietal cortex in perceptual learning (Eureka effect): an interference approach using rTMS

The neural mechanisms underlying perceptual learning are still under investigation. Eureka effect is a form of rapid, long-lasting perceptual learning by which a degraded image, which appears meaningless when first seen, becomes recognizable after a single exposure to its undegraded version. We used online interference by focal 10-Hz repetitive transcranial magnetic stimulation (rTMS) to evaluate whether the parietal cortex (PC) is involved in Eureka effect, as suggested by neuroimaging data. RTMS of the PC did not affect recognition of degraded pictures when displayed 2s after the presentation of their undegraded version (learning phase). However, rTMS delivered over either right or left intraparietal sulcus simultaneously to the undegraded image presentation, disrupted identification of the degraded version of the same pictures when displayed 30 min after the learning phase. In contrast, recognition of degraded images was unaffected by rTMS over the vertex or by sham rTMS, or when rTMS of either PC was delivered 2s after the presentation of the undegraded image. Findings strongly support the hypothesis that both PC at the level of the intraparietal sulcus play a pivotal role in the Eureka effect particularly in consolidation processes, and contribute to elucidate the neural network underlying rapid perceptual learning.