Characteristics of non-verbal memory impairment in bipolar disorder: the role of encoding strategies

Background. There is evidence that individuals with bipolar disorder exhibit neuropsychological impairments not only during episodes of depression or mania but also when they are euthymic. One of the most consistently reported cognitive problems in euthymic individuals with bipolar disorder is impairment in episodic memory. Learning and memory depend on individuals' ability to organize information during learning. A recent study by our group showed that verbal episodic memory impairments in euthymic patients with bipolar I disorder (BP-I) are mediated by difficulties in organizing verbal information appropriately during learning. The purpose of the present study was to determine whether memory impairments in euthymic individuals with BP-I extend to non-verbal memory and whether non-verbal memory impairments are mediated by difficulties in organizing non-verbal information during encoding. Method. Study participants were 25 euthymic, remitted individuals with BP-I and 25 age, gender and education matched control participants. Participants completed the Rey-Osterrieth Complex Figure Test (RCFT), a well-established measure of non-verbal memory that enables assessment of organization during learning. Results. Compared to control participants, BP-I participants showed impaired performance on the RCFT immediate recall. They also relied less on organizational strategies during encoding. Multiple regression modeling indicated that group differences between control and BP-I participants in long-delayed free recall did not remain statistically significant when effects of lower organization were partialled out. Conclusions. Non-verbal memory problems in individuals with bipolar disorder, while euthymic, are mediated by poor use of non-verbal organization strategies during encoding, but do not appear to reflect deficits in retention of information.