Neutral auditory words immediately followed by painful electric shock show reduced next-day recollection

In this study, we investigated the effect of experimentally delivered acute pain on explicit and implicit memory. Twenty-five subjects participated in experimental sessions on consecutive days. The first session involved a categorization task intended to induce incidental memory encoding. There were two conditions, presented in randomized order, in which subjects listened to a series of words, which was repeated three times. In one condition, one-third of the word items were immediately followed by a painful electrical shock and these pain-paired items were presented unpredictably. In the other condition, all word items were not associated with pain. Response times over these repeated presentations were assessed for differences. Explicit memory was tested the following day, employing a Remember-Know assessment of word recognition, with no shocks employed. Recollection was significantly reduced for pain-paired words, as the proportion of correct Remember responses (out of total correct responses) was significantly lower. There were no significant reductions in memory for non-pain items that followed painful stimulation after a period of several seconds. Consistent with the experience of pain consuming working memory resources, we theorize that painful shocks interrupt memory encoding for the immediately preceding experimental items, due to a shift in attention away from the word item.