Autonomic nervous system arousal and cognitive functioning in bipolar disorder.

OBJECTIVE

Previous theories about the etiology of cognitive dysfunction in bipolar disorder (BD) emphasized trait factors such as neurological impairment. State factors, other than mood symptoms, that may exacerbate functional deficits have not yet been considered. The purpose of this study was to examine autonomic nervous system (ANS) arousal following cognitive challenge. The study compared patients with BD and healthy controls (HC) in physiological measures and neuropsychological test scores.

METHODS

Thirty euthymic patients with BD and 22 HC completed the study. Participants completed mood [Beck Depression Inventory-II (BDI-II) and Young Mania Rating Scale (YMRS)], anxiety (State-Trait Anxiety Inventory), and substance abuse (Drug Abuse Screening Test-20 item and Alcohol Use Disorders Identification Test) measures. They were connected to an electrogram, a sensitive thermometer for measuring finger temperature, and electrodes that measure galvanic skin response. After a five-min baseline measurement in a restful state, participants completed a computerized neuropsychological battery (CNS Vital Signs).

RESULTS

The group with BD reported significantly more mood symptoms (BDI-II, t = 3.71, p < 0.001; YMRS, t = 6.73, p < 0.001) and scored higher on a measure of trait-anxiety (State-Trait Anxiety Inventory, t = 2.91, p < 0.001) than HC. A multivariate analysis of variance revealed higher arousal on all physiological measures in the BD group relative to HC at baseline [F(3,48) = 13.1, p < 0.001] and during cognitive testing [F(3,48) = 11.3, p < 0.001]. The increase in physiological arousal from a restful state to the time of testing was higher for the BD group [F(3,37) = 8.06, p < 0.001]. With respect to cognitive data, HC scored higher than patients with BD across the measures of memory (F = 8.5, p < 0.001), sustained (F = 9.5, p < 0.001) and complex (F = 2.7, p < 0.04) attention, processing speed (F = 10.0, p < 0.001), reaction time (F = 7.8, p < 0.001), cognitive flexibility (F = 19.7, p < 0.001), working memory (F = 10.8, p < 0.001), and social acuity (F = 5.7, p < 0.01), with partial eta-squared from 0.18 to 0.62. Correlational analysis revealed significant associations between various cognitive test scores and changes in physiological arousal from baseline to testing (-0.59 ≤ r ≤ 0.22).

CONCLUSIONS

Relative to HC, patients with BD experience larger changes in ANS arousal between a restful baseline and cognitive testing, and achieve lower cognitive test scores. Further research is needed to determine whether acute physiological symptoms of anxiety directly compromise cognitive functioning in BD.