Distinct neural signatures underlying information manipulation in working memory

Working memory is a core cognitive ability that supports both the maintenance and manipulation of information in mind to serve complex behavior. Previously, stimulus representation in memory maintenance has been observed in both voltage and alpha-band activity in electroencephalography (EEG). However, the exact function of these two neural signatures in working memory has remained elusive. Here we systematically examined this question by asking whether memory manipulation is supported by the same neural signatures as memory maintenance. Human participants either maintained a previously-seen spatial location, or manipulated the spatial location according to a mental rotation cue over a delay. Using multivariate distance-based decoding, we observed robust neural representations of maintained and manipulated locations in both low-frequency voltage and alpha-band oscillatory activity, suggesting that memory maintenance and manipulation are supported by multiple overlapping neural signatures in EEG. Yet, these neural signatures demonstrated distinct spatiotemporal dynamics: location representations in alpha-band activity were most evident in the posterior channels, while location representations in voltage were most evident in the more anterior, central channels. The temporal emergence of manipulated representation in central voltage also preceded that in posterior alpha-band activity, suggesting that voltage might carry stimulus-specific source signals originated internally from more anterior cortex, whereas alpha-band activity might reflect feedback signals in posterior cortex received from higher-order cortex. Lastly, while location representations in both signals could be compressed into a low-dimensional neural subspace, location representation in central voltage was higher-dimensional and underwent a representational transformation that exclusively predicted memory behavior. Together, these results highlight the crucial role of central voltage in memory manipulation, as well as offer direct experimental evidence supporting functional distinction between voltage and alpha-band oscillatory activity in EEG.