Induction and measurement of episodic memories in healthy adults

Episodic memory is that part of our memory which enables us to memorize a personal event (what) in terms of place (where) and time (when). It is expressed on verbal and behavioral level. In this report we describe a novel method to induce de novo episodic memories in humans for unique events in the laboratory and measure them with standardized ratings and non-verbal motor responses. Visual stimuli were hidden in four out of eight quadrants on a computer screen. Each of these quadrants could be highlighted by pushing a corresponding button on a keyboard which either revealed a visual stimulus for 100 ms or remained black. Participants had to remember on which occasion (when) and at which position (where) a specific picture (what) has been encountered. Healthy adult participants were able to verbally recollect the details and the spatiotemporal context of visual stimuli with combinations of high or low concreteness and neutral or emotional content after retention delays up to 72 h. The mean number of button presses to each of the four quadrants containing visual stimuli was positively correlated with verbal episodic memory performance. We conclude that episodic memories can be induced experimentally and can be measured by exploratory button press behavior which can serve as a non-verbal behavioral correlate of episodic memory performance.