EEG biomarkers of free recall.

• Increased theta (4–8 Hz), decreased alpha (8–20 Hz), and increased gamma (40–128 Hz) power appear in the moments immediately preceding spontaneous recall of context-dependent, long-term memories. • This pattern of increased theta, decreased alpha, increased gamma appears more strongly when recalling memories after a delay of one or more days than when recalling memories after just a few seconds. This comparison between immediate and delayed recall helps to minimize the contribution of motor-related EEG signals that may accompany vocal recall. • These spectral biomarkers of memory retrieval preceding spontaneous recall contributes to an emerging body of evidence demonstrating the utility of non-invasive recording methods for decoding cognitive states. Brain activity in the moments leading up to spontaneous verbal recall provide a window into the cognitive processes underlying memory retrieval. But these same recordings also subsume neural signals unrelated to mnemonic retrieval, such as response-related motor activity. Here we examined spectral EEG biomarkers of memory retrieval under an extreme manipulation of mnemonic demands: subjects either recalled items after a few seconds or after several days. This manipulation helped to isolate EEG components specifically related to long-term memory retrieval. In the moments immediately preceding recall we observed increased theta (4–8 Hz) power (+ T), decreased alpha (8–20 Hz) power (-A), and increased gamma (40–128 Hz) power (+ G), with this spectral pattern (+ T - A + G) distinguishing the long-delay and immediate recall conditions. As subjects vocalized the same set of studied words in both conditions, we interpret the spectral + T - A + G as a biomarker of episodic memory retrieval. [ABSTRACT FROM AUTHOR]