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PLoS Biol. 2018 Aug 15;16(8):e2003805. doi: 10.1371/journal.pbio.2003805. eCollection 2018 Aug.

Serial representation of items during working memory maintenance at letter-selective cortical sites.

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Department of Psychiatry, Academic Medical Center, Amsterdam, The Netherlands.
Radboud University, Donders Institute for Brain, Cognition and Behaviour, Nijmegen, The Netherlands.
Centre for Human Brain Health, School of Psychology, University of Birmingham, Birmingham, United Kingdom.
Department of Biomedical Engineering, Columbia University, New York City, New York, United States of America.
Volen Center for Complex Systems, Brandeis University, Waltham, Massachusetts, United States of America.


A key component of working memory is the ability to remember multiple items simultaneously. To understand how the human brain maintains multiple items in memory, we examined direct brain recordings of neural oscillations from neurosurgical patients as they performed a working memory task. We analyzed the data to identify the neural representations of individual memory items by identifying recording sites with broadband gamma activity that varied according to the identity of the letter a subject viewed. Next, we tested a previously proposed model of working memory, which had hypothesized that the neural representations of individual memory items sequentially occurred at different phases of the theta/alpha cycle. Consistent with this model, the phase of the theta/alpha oscillation when stimulus-related gamma activity occurred during maintenance reflected the order of list presentation. These results suggest that working memory is organized by a cortical phase code coordinated by coupled theta/alpha and gamma oscillations and, more broadly, provide support for the serial representation of items in working memory.

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