The perfect time to be stressed: a differential modulation of human memory by stress applied in the morning or in the afternoon.

We measured the effects of a stressful experience on memory for emotionally arousing and neutral material learned after exposure to a stressor which induces a significant increase in corticosteroid stress hormones. Because memory performance can be influenced by circadian changes in corticosteroid levels, subjects were tested either in the morning or in the afternoon. Nineteen healthy men (9 in the morning group and 10 in the afternoon group) were submitted to a psychological stress task before viewing a story composed of emotionally negative and neutral segments, while another 20 healthy males (10 in the morning group and 10 in the afternoon group) viewed the story without being exposed to the psychological stressor.