Brain oscillatory analysis of visual working memory errors

Mapelli, Igor
Brain dynamics of memory formation were explored throughout a working memory (WM) task. Electroencephalography data were acquired from participants while presented with grayscale photos of object categories (each category defined by images sharing a common gist). Following a short delay, two probes were shown to test memory accuracy. Time-frequency representations of successful and erroneous memories were contrasted. Additionally, brain connectivity was studied via coherency and phase-amplitude coupling (PAC). Where significant differences were identified, oscillatory properties of false memories (a novel item of the same category recognized as familiar) were compared with those of successful and erroneous memories. Spectral analysis revealed occipital theta power for encoding of successful and false memories to be smaller when compared to other memory errors. The reduced theta power indicates successful encoding and reflects efficient activation of the underlying neural assemblies. During the retention interval, prominent alpha-beta activity over right parieto-occipital channels was found to be larger for false memories and errors when compared to correct responses. High levels of alpha-beta oscillatory activity for errors indicate poor maintenance leading to inefficient allocation of WM resources. For false memories, they imply necessary cognitive effort to manage an extra semantic and perceptual load induced during encoding. Significant fronto-occipital coherency was measured: Possibly, theta and alpha band coherency reflect central executive functions of WM, whereas beta band coherency indicates coordination of local assemblies related to stimulus representations. Significant theta/gamma PAC, linked to WM retention of sequentially encoded stimuli, and alpha/gamma PAC, reflecting processing of visuo-spatial information, were also observed.