The effect of seasons and seasonal variation on neuropsychological test performance in patients with bipolar I disorder and their first-degree relatives.

Background: Bipolar disorder (BD) patients have cognitive deficits that may remain in the euthymic phase. Similar although milder cognitive deficits may be found in their first-degree relatives. We wanted to analyze whether the self-report of seasonality, the season when individuals were tested or the circadian preference influences the neuropsychological test performance measured in the familial BD, type I, patients and their healthy first-degree relatives.

Method: A structured diagnostic interview (SCID) and neuropsychological test battery were administered to 32 familial BD type I patients, 40 of their unaffected first-degree relatives and 50 controls, all from population-based samples. BD patients and their relatives filled in the Seasonal Pattern Assessment Questionnaire (SPAQ) and the Horne-Östberg Morningness-Eveningness Questionnaire (MEQ).

Results: Individuals, who reported that seasonal variation was a problem, scored worse on the measures of visuoconstructional functions, visuospatial reasoning, auditory attention and working memory, and verbal memory than those with no seasonal variation. The season when tested had an influence on test performance. Individuals from the families that were tested in spring, summer and autumn scored better than those tested in winter on the measures of visual and verbal attention, working memory, verbal ability, verbal fluency, and executive functioning. Among the controls there was no difference in the test scores from season to season. The circadian preference had no effect on test performance.

Limitations: Only relatives, not BD patients were tested in winter.

Conclusion: Seasonal variation in mood and behavior as a problem in patients and their first-degree relatives influences negatively the neuropsychological test performance. In addition, among the patients and first-degree relatives the neuropsychological test performance in winter may be worse than in other seasons.