Memory for pain: recalling the quality and intensity of expected acute pain.

Abstract

This thesis reports a series of studies designed to assess the extent to which the intensity and qualitative nature of expected acute pain events can be recalled. The first preliminary study assessed recall of the intensity and quality of postoperative pain following day surgery for varicose vein removal. Twenty four participants reported their expectations of pain, their actual pain experiences and their retrospective ratings of pain using the Short Form McGill Pain Questionnaire (SF-MPQ) and a VAS to report pain intensity. In line with prior research, recollections of pain quality appeared to be less accurate than the retrospective ratings of pain intensity. In the second preliminary study, 50 participants who had never experienced vascular surgery were required to provide estimates of the likely nature of postoperative pain following varicose vein removal, based on the information provided in one of two patient information leaflets. Although both groups of non-patient participants overestimated the intensity of the pain, both provided estimates of the qualitative nature of the pain that were similar to the reports made by the patient participants. These preliminary studies highlighted the limitations of prior research which has inferred pain recall accuracy by simply by comparing descriptions of acute pain made whilst in pain with ratings made retrospectively, and demonstrated the need to employ a more direct method of assessing memory for pain. The preliminary studies also highlighted the need to consider the influence of the participants ’ expectations of the likely nature o f a forthcoming pain and levels of anxiety on memory for pain. Finally, investigating the relative extent to which pain can be recalled relative to another sensory experience was deemed to be necessary. The main study for this thesis assessed memory for experimentally induced acute pain using the remember/know research paradigm (see Tulving, 1985). In Part One of this study, Cold Pressor (CP) pain was induced in 97 participants who provided ratings of their expectations of the CP pain, followed by reports of their actual pain experiences using the MPQ and a VAS whilst using the CP. Participants also provided ratings of anxiety and used a list of 57 descriptors to report the taste of an unusual drink. In Part Two of the study, two weeks later, participants provided retrospective ratings of the CP pain using the MPQ and a VAS, ratings of anxiety, and the taste of the drink. Participants were then asked to make ‘remember’ or ‘know ’judgements about the MPQ pain and taste descriptors that they had selected, based on the level of conscious awareness accompanying their recollections. The findings indicate that memory for the intensity of expected acute pain was reliable for at least two weeks. In addition, the data suggest that recollections of the broad defining aspects of the quality of acute pain can also be reliable, but may be more appropriately assessed at a ‘type of pain’ level rather than the fine-grained level of individual MPQ descriptors. Central to this investigation was the finding that participants were readily able to distinguish between whether their recollections reflected ‘remembering’ and ‘knowing’ about their prior experiences of both pain and taste. It is concluded that the use of the remember/know distinction allows for a more direct assessment of the participants ’ reports of their memories than inferring the likely nature of these recollective experiences, and that recollections of pain and of other sensory experiences are broadly similar. Expectations and anxiety were not related to pain recall accuracy.