Mentally healthy controls without a family history of mood disorders showed no such seasonal variation, suggesting a genetic component to the process of thought.
Studies show that neuropsychological impairments in bipolar disorder are not restricted to mood episodes but may also be present in euthymic individuals (those of normal mood) and include executive functioning — a set of mental processes that help connect past experience with present action — verbal memory, attention, and processing speed deficits.
Meanwhile, there is evidence of seasonal variation in mood and behavior as well as abnormalities in circadian preference in bipolar disorder.
Elina Rajajärvi of the National Institute for Health and Welfare, Helsinki and colleagues administered a structured diagnostic interview and neuropsychological test battery to 122 people. Thirty-two of them had familial bipolar I disorder, 40 were unaffected first-degree relatives of the bipolar I patients, and 50 were mentally healthy controls. All of them were taken from population-based samples.
Bipolar disorder patients and their relatives filled in the Seasonal Pattern Assessment Questionnaire (SPAQ) and the Horne–Östberg Morningness– Eveningness Questionnaire (MEQ).
Among bipolar disorder patients and their relatives, those who reported seasonal variations in mood and behavior scored worse on the measures of visuoconstructional function (ability to manipulate spatial information into a design), visuospatial reasoning (the ability to understand visual representations of objects and their spatial relationships), auditory attention (ability to listen long enough to complete a task) and working memory, and verbal memory than those with no seasonal variation.
The season when a neuropsychological test battery was administered was associated with test performance. Patients and relatives tested in spring, summer or fall performed better than in winter in measures of visual and verbal attention and working memory, verbal ability, verbal fluency and executive functioning.
By contrast, there was no association between season and test scores among the mentally healthy controls.
“In studying cognitive endophenotypes (biological marker) of bipolar disorder it may be warranted to take the seasonal variation of the test performance and the possible seasonal variation in mood and behavior into account when the neuropsychological examination is done,” Rajajärvi et al conclude in the Journal of Affective Disorders.
Source: Medwire News