Impulsivity is associated with abnormal patterns of neural changes in bipolar disorder patients, with the anterior cingulate cortex (ACC) potentially involved in altered impulsivity regulation, research shows.

Euthymic, manic, and depressed bipolar disorder patients all show greater impulsivity than healthy individuals, and the trait is linked to clinical outcomes and risky behaviors. In a previous study, the team, led by Jair Soares from the University of Texas Health Sciences Center at Houston, USA, found that impulsivity is inversely related to orbitofrontal cortex (OFC) volume in healthy individuals.

Building on these findings, they administered the Barratt Impulsiveness Scale (BIS) version 11A to 63 patients with bipolar disorder, as well as the Hamilton Rating Scale for Depression (HAM-D) and the Young Mania Rating Scale (YMRS).

In addition, the participants completed a clinical interview and underwent magnetic resonance imaging to measure gray and white matter volumes in the OFC, ACC, medial prefrontal cortex, and amygdala, all of which are linked to bipolar disorder pathophysiology, the team notes in the journal Bipolar Disorders.

The average age of the patients was 38.2 years. In all, 44 patients were diagnosed with bipolar I disorder and the remainder with bipolar II disorder. Comorbid anxiety disorders were identified in 26 patients.

The average HAM-D score was 14.2, while that of the YMRS was 5.9. Twenty one patients were remitted, 32 depressed, seven manic or hypomanic, and three in a mixed state. The average total BIS score was 77.1, at 30.3 for nonplanning, 25.5 for motor, and 21.3 for attention subscales. This compares with a total BIS score of 64.2 for the general population, as derived from a previously published normative study.

MRI whole-brain analysis revealed that only the gray matter volume of the left rostral ACC was significantly inversely correlated with the BIS total scores. These findings were confirmed by small-volume false discovery rate correction. No other significant white or gray matter volume correlations with total BIS scores were detected.

Interestingly, further analysis revealed that left rostral ACC gray matter volumes were significantly inversely correlated only with BIS motor subscale scores, not with either the attention or nonplanning subscales. The findings were unaffected by any clinical variables included in the analysis.

The team writes: “The current study provides the novel finding that rostral ACC volumes are inversely associated with impulsivity, particularly motor impulsivity, in bipolar disorder patients.”

They add: “These results suggest that the ACC may participate in the neurocircuitry that regulates abnormal impulsivity in bipolar disorder patients, and the function of this neurocircuitry in bipolar disorder may be different from that in healthy volunteers.”

MedWire (www.medwire-news.md) is an independent clinical news service provided by Current Medicine Group, a part of Springer Science+Business Media. © Current Medicine Group Ltd; 2009

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