Time dependent effects of stress prior to encoding on event-related potentials and 24 h delayed retrieval

Stress can exert profound effects on memory encoding. Here, we investigated whether (sub)cortical information processing during encoding and memory retrieval at a 24 h delayed test are affected by the temporal proximity between stress and memory encoding. Sixty-four participants engaged in the Maastricht Acute Stress Test (MAST) or a no-stress control condition either immediately before (i.e., proximate condition) or 30 min before (i.e., distant condition) a picture encoding task. In general, stress decreased the number of freely recalled and recognized pictures and increased the number of false alarms. However, timing of stress exposure did not differentially affect picture recall, recognition or selective attention processes (i.e., LPP). Nevertheless, stress-induced cortisol responses and correctly recognized neutral pictures were positively associated within the proximate stress condition but negatively associated within the distant stress condition. These findings suggest that the time at which a stressor is applied might differentially impact the association between stress-induced cortisol elevations and memory formation and indicate the need for a finer delineation of the time window during which glucocorticoids affect memory formation processes. (C) 2013 Elsevier Ltd. All rights reserved.