Sleep and cognitive function in bipolar disorder

Abstract

People with bipolar disorder (BD) suffer from cognitive dysfunction during all phases of the disorder including euthymia but its origin is unknown. Experimental sleep studies and evidence from people with clinical sleep disorders has demonstrated an association between sleep disruption and cognitive dysfunction. Clinically significant sleep disturbances are common across the course of BD including euthymia but little is known about their association with cognitive function. Methods BD patients (n=46) in any mood state and healthy controls (n=42) without known sleep abnormalities were tested cognitively and had comprehensive sleep/circadian rhythm assessment, mood, function and quality of life (QoL) assessed over a 21 day period with actigraphy, respiratory sleep studies and rating scales. Abnormal sleep phenotypes were identified from objective sleep variables including long/short sleepers and those with sleep patterns indicative of a circadian rhythm disorder (CRD). The relationship between sleep, mood, QoL and cognition was explored. Results Objectively assessed sleep abnormalities including long sleep, CRD and obstructive sleep apnoea were common in BD patients. BD patients with objectively defined sleep abnormalities had worse psychosocial function and QoL than BD normal sleepers, independent of mood. Only BD abnormal sleepers ii performed significantly worse than controls on cognitive tasks of attention, executive control, processing speed and aspects of verbal learning and had increased intra-individual variability in attentional response times. BD normal sleepers did not differ cognitively from controls. The majority of these effects were independent of mood. Conclusions Sleep abnormalities are common in BD patients and are associated with impairments in attention, executive control, processing speed and verbal learning. Sleep disturbances are an important therapeutic target in BD and improvement in sleep may lead to improved psychosocial and cognitive function.