Patients with bipolar disorder commonly report problems with cognition, especially concentration and memory. Neuropsychological studies show significant impairments in declarative memory, during both acute mood episodes and in euthymic phase. The hippocampus is known to be involved in the formation of declarative memories. The hippocampus in patients with bipolar disorder has been subject to further investigation. Imaging studies have yielded inconsistent results concerning hippocampal structure and function in patients with bipolar disorder. There are many possible reasons for the inconsistency. One suggested confounder is medications.
In this paper we look at evidence for the role of the hippocampus in (declarative) memory and investigate neuroimaging studies that examine hippocampal (dys-)function in patients with bipolar disorder. Possible effects of medications on cognition (and memory) and the hippocampus are discussed. Lastly, we discuss the most commonly used medications’ possible mechanisms of action in the brain. It may be important to try and separate medicated and unmedicated groups with bipolar disorder in future studies.