Objectives: Individuals with bipolar disorder exhibit neuropsychological impairments when they are euthymic (neither depressed nor manic). One of the most consistently reported cognitive problems in euthymic individuals with bipolar disorder is impairment in verbal episodic memory. Recent findings suggest that episodic memory difficulties in these individuals are attributable to difficulties using organizational strategies during encoding. The purpose of the present study was (i) to investigate whether difficulties using organizational strategies in bipolar disorder are due to a failure in spontaneously initiating verbal organization strategies or are due to difficulties implementing such strategies, and (ii) to compare the characteristics of verbal organizational impairment in bipolar disorder with those observed in individuals with obsessive-compulsive disorder (OCD).
Methods: Study participants were 20 individuals with bipolar I disorder (BP-I), 20 individuals with OCD, and 20 healthy control participants matched for age, gender, and education. Participants completed a verbal encoding paradigm that involved spontaneous and directed use of verbal organization strategies during encoding of word lists.
Results: Compared with control subjects, both BP-I and OCD participants showed impaired verbal organization in the spontaneous encoding condition. In the directed encoding condition, OCD patients organized the word lists as well as control participants whereas BP-I participants exhibited lower verbal organization than both control and OCD participants. OCD and BP-I participants' free recall performance did not differ from that of control participants in the spontaneous encoding condition. In the directed encoding condition, BP-I participants recalled fewer words than OCD or control participants.
Conclusions: Episodic memory difficulties in OCD are associated with difficulties spontaneously initiating verbal organization strategies during encoding whereas the ability to implement verbal organization when instructed to do so is preserved. BP-I participants, on the other hand, exhibit difficulties in both spontaneously initiating verbal organization strategies and in the ability to implement such strategies when instructed to do so.