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Chong Zhao, Keisuke Fukuda, Geoffrey Woodman; Ruling out a role for oscillatory coupling of frontal theta and posterior alpha in visual long-term memory encoding. Journal of Vision 2021;21(9):2423. doi: https://doi.org/10.1167/jov.21.9.2423.
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© ARVO (1962-2015); The Authors (2016-present)
Given that visual memories are stored in regions spanning the cortex and subcortex, visual memory encoding is one of the most likely cognitive processes to rely on the coordinated coupling of activity through the synchronization of neural oscillations. Previous research suggests that decreasing posterior alpha power and increasing mid-frontal theta power individually contribute to better visual long-term memory encoding. Naturally, a possible explanation for this observation would be that the frontal theta enhancement and posterior alpha suppression form a coherent network for successful memory encoding in which the higher frequency alpha activity is coupled to the slower theta carrying wave. Contrary to this hypothesis, here we show that neither the amplitude-amplitude coupling nor the phase-amplitude coupling between frontal theta and posterior alpha appears underlie observers’ ability to encode pictures into long-term visual memory. First, we found that the strength of coupling was not predictive of observers’ subsequent memory recognition ability. Second, the theta-alpha coupling relationships were not modified by anodal transcranial direct current stimulation over temporal lobe, despite brain stimulation improving memory for pictures of objects. Third, when we measured raw correlations between alpha and theta power, we discovered that posterior alpha power and frontal theta power were more tightly correlated during eyes-open resting state than during memory encoding, when the coordination between theta and alpha breaks down. Together, these findings show that posterior alpha and frontal theta power are individually related to visual long-term memory encoding, but this is not due to large scale coupling between these brain oscillations.
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