A neural decision signal during internal sampling from working memory

How humans transform sensory information into decisions that steer purposeful behaviour is a central question in psychology and neuroscience that is traditionally investigated during the sampling of external sensations. The decision-making framework of gradual information sampling toward a decision has been proposed also to apply when sampling internal sensory evidence from memory. However, neural evidence for this proposal remains lacking. Here we report that sampling internal visual representations from working memory elicits a scalp-EEG potential associated with gradual evidence accumulation - the Central Parietal Positivity (CPP). Consistent with an evolving decision process, we show how this signal (i) builds up to, and scales with, the time participants require to reach a decision about the cued memory content and (ii) is amplified when having to select (decide) among multiple contents in working memory. These results bring the electrophysiology of decision making into the domain of working memory and suggest that variability in memory-guided behaviour may be driven (at least in part) by variations in the sampling of our inner mental contents.