Psychogenic amnesia: syndromes, outcome, and patterns of retrograde amnesia.

There are very few case series of patients with acute psychogenic memory loss (also known as dissociative/functional amnesia), and still fewer studies of outcome, or comparisons with neurological memory-disordered patients. Consequently, the literature on psychogenic amnesia is somewhat fragmented and offers little prognostic value for individual patients. In the present study, we reviewed the case records and neuropsychological findings in 53 psychogenic amnesia cases (ratio of 3:1, males:females), in comparison with 21 consecutively recruited neurological memory-disordered patients and 14 healthy control subjects. In particular, we examined the pattern of retrograde amnesia on an assessment of autobiographical memory (the Autobiographical Memory Interview). We found that our patients with psychogenic memory loss fell into four distinct groups, which we categorized as: (i) fugue state; (ii) fugue-to-focal retrograde amnesia; (iii) psychogenic focal retrograde amnesia following a minor neurological episode; and (iv) patients with gaps in their memories. While neurological cases were characterized by relevant neurological symptoms, a history of a past head injury was actually more common in our psychogenic cases (P = 0.012), perhaps reflecting a 'learning episode' predisposing to later psychological amnesia. As anticipated, loss of the sense of personal identity was confined to the psychogenic group. However, clinical depression, family/relationship problems, financial/employment problems, and failure to recognize the family were also statistically more common in that group. The pattern of autobiographical memory loss differed between the psychogenic groups: fugue cases showed a severe and uniform loss of memories for both facts and events across all time periods, whereas the two focal retrograde amnesia groups showed a 'reversed' temporal gradient with relative sparing of recent memories. After 3-6 months, the fugue patients had improved to normal scores for facts and near-normal scores for events. By contrast, the two focal retrograde amnesia groups showed less improvement and continued to show a reversed temporal gradient. In conclusion, the outcome in psychogenic amnesia, particularly those characterized by fugue, is better than generally supposed. Findings are interpreted in terms of Markowitsch's and Kopelman's models of psychogenic amnesia, and with respect to Anderson's neuroimaging findings in memory inhibition.

Performance of Decorticated Rats on Fixed Interval and Fixed Time Schedules.

Rats with neocortex totally removed (decorticates), rats with hippocampal lesions (hippocampals), and their surgical controls, were trained on a fixed interval (FI) 40 s schedule, where the first bar-press response made more than 40 s after a previous reinforcement was rewarded. The decorticates and hippocampals adopted similar patterns of behaviour to the control groups through there were between-group differences in the details of performance. Compared to controls the hippocampals showed shorter post-reinforcement pauses and faster overall rates of responding, whilst the reverse was true of the decorticates. Some of this performance difference in the decorticates was attributed to difficulty in retrieving and consuming solid food reinforcement. The performance of the decorticates and hippocampals, as reflected by the post-reinforcement pause, response distribution and running rate as a function of post-reinforcement pause duration, suggests that timing remains operational in both groups. The differences in response profiles between the two experimental groups, however, indicate that hippocampus and neocortex probably make independent contributions to performance in this situation. The decorticates and their control group were later transferred from the FI to a response-independent fixed time (FT) 40 s schedule. Both groups then returned to the former FI 40 s schedule. The decorticates adjusted their behaviour to the different schedules in the same way as the control animals. The results overall are consistent with previous findings that decortication does not abolish normal patterns of operant learning and extends them to include temporal schedules.