Psychological theories of memory posit that when people recall a past event, they not only recover the features of the event itself, but also recover information associated with other events that occurred nearby in time. The events surrounding a target event, and the thoughts they evoke, may be considered to represent a context for the target event, helping to distinguish that event from similar events experienced at different times. The ability to reinstate this contextual information during memory search has been considered a hallmark of episodic, or event-based, memory. We sought to determine whether context reinstatement may be observed in electrical signals recorded from the human brain during episodic recall. Analyzing electrocorticographic recordings taken as 69 neurosurgical patients studied and recalled lists of words, we uncovered a neural signature of context reinstatement. Upon recalling a studied item, we found that the recorded patterns of brain activity were not only similar to the patterns observed when the item was studied, but were also similar to the patterns observed during study of neighboring list items, with similarity decreasing reliably with positional distance. The degree to which individual patients displayed this neural signature of context reinstatement was correlated with their tendency to recall neighboring list items successively. These effects were particularly strong in temporal lobe recordings. Our findings show that recalling a past event evokes a neural signature of the temporal context in which the event occurred, thus pointing to a neural basis for episodic memory.EEG | electrocorticography | oscillations | free recall | contiguity T he pivotal distinction between memory for facts (semantic memory) and memory for episodes or experiences (episodic memory) has been argued to reflect, at least in part, the reinstatement of a gradually changing context representation that reflects not only external conditions, but also an ever-changing internal context state (1, 2). According to this view, the unique quality of episodic memory is that in remembering an episode, we partially recover its associated mental context, and that this context information conveys some sense of when the experience took place, in terms of its relative position along our autobiographical time line.A number of laboratory memory tasks rely on episodic memory, including experimenter-cued tasks (e.g., item recognition and cued recall) and self-cued tasks (e.g., free recall). Performing these episodic memory tasks requires distinguishing the current list item from the rest of one's experience. According to early theories of episodic memory (e.g., 3, 4), context representations are composed of many features that fluctuate from moment to moment, gradually drifting through a multidimensional feature space. These contextual features may reflect environmental cues, recently studied items, participants' internal mental states, or may evolve randomly over time. During recall, the context representation forms part of th...