Patients with bipolar disorder have impaired recall of episodic autobiographical memories when recounting events that occurred during mania, report Canadian researchers.
Bipolar patients were also more likely to recall memories from an observer's perspective than healthy individuals, the authors note.
The team used the Autobiographic Interview to assess 20 bipolar disorder patients and 20 age- and gender-matched healthy controls without a history of mental disorder.
They asked patients with bipolar disorder to provide detailed accounts of three events in the past 2 years that occurred during a manic, depressed, and euthymic mood state, while control participants recalled memories from a positive, sad, and neutral state. The authors then dissociated episodic and non-episodic aspects of the memories and analyzed the perspective from which they were recalled.
Both patients and controls recalled more episodic than non-episodic details. However, patients with bipolar disorder reported significantly fewer episodic details for events encoded during manic states than controls in a positive mood state.
By contrast, there was no significant difference in recall of events that occurred during depressed and euthymic mood states in comparison with controls in sad and neutral states, and there was no association between the recall of non-episodic details and mood state.
The team also found that bipolar disorder patients reported re-experiencing significantly less vivid and auditory sensations for events encoded during mania than did healthy controls for events encoded in a positive mood state, suggesting that patients had some insight into this phenomenon.
Importantly, there was no relationship between the positivity (valence) of the memory and episodic or non-episodic memory performance in either group, suggesting that the authors' findings were due to mood state and not the nature of the memory itself.
Interestingly, bipolar disorder patients were significantly more likely to recall events from a third-person, observer standpoint than controls. Overall, patients with bipolar disorder recalled memories from this perspective 37% of the time, compared with just 13% for healthy controls.
"At present, we are unable to adjudicate as to whether the selective episodic memory deficit for events encoded during mania reported here stems from poor encoding at the time of event occurrence or from a retrieval deficit at the time of testing," explains Margaret McKinnon, from McMaster University in Hamilton, Ontario, and colleagues in the journal Psychiatry Research.
Further research will be needed to determine this, as well as to explore how disease severity affects the reported associations, they conclude.
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