Prefrontal hyperactivation during working memory task in untreated individuals with major depressive disorder.

The prefrontal cortex, a part of the limbic-thalamic-cortical network, participates in regulation of mood, cognition and behavior and has been implicated in the pathophysiology of major depressive disorder (MDD). Many neuropsychological studies demonstrate impairment of working memory in patients with MDD. However, there are few functional neuroimaging studies of MDD patients during working memory processing, and most of the available ones included medicated patients or patients with both MDD and bipolar disorder. We used functional magnetic resonance imaging (fMRI) to measure prefrontal cortex function during working memory processing in untreated depressed patients with MDD. Fifteen untreated individuals with Diagnostic and Statistical Manual of Mental Disorders-Fourth Edition recurrent MDD (mean age+/-s.d.=34.3+/-11.5 years) and 15 healthy comparison subjects (37.7+/-12.1 years) matched for age, sex and race were studied using a GE/Elscint 2T MR system. An echo-planar MRI sequence was used to acquire 24 axial slices. The n-back task (0-back, 1-back and 2-back) was used to elicit frontal cortex activation. Data were analyzed with a multiple regression analysis using the FSL-FEAT software. MDD patients showed significantly greater left dorsolateral cortex activation during the n-back task compared to the healthy controls (P<0.01), although task performance was similar in the two groups. Furthermore, the patients showed significant anterior cingulate cortex activation during the task, but the comparison subjects did not (P<0.01). This study provides in vivo imaging evidence of abnormal frontolimbic circuit function during working memory processing in individuals with MDD.

Impulsivity and bipolar disorder.

Impulsivity is frequently associated with bipolar disorder (BD) during manic episodes, but may also be present in euthymic bipolar patients. Aggression is an impulsivity-related behavior also found during manic episodes. The objective of this review is to further clarify the relationship between impulsivity and BD. A search in Medline and Psycinfo databases, combined with a manual search of selected references, was conducted to identify available literature on BD and impulsivity-related features. Although few studies have directly measured impulsivity in BD, available findings suggest that impulsivity is not only state-related, but also a trait component of BD, which could represent a core feature of the illness. Further research exploring the neurobiology of the impulsivity/BD relationship may contribute to elucidate the pathophysiology and to improve the diagnosis and treatment of this severe illness.

Trait impulsivity in patients with mood disorders.

BACKGROUND: Impulsivity is a key component of the manic behavior of bipolar disorder and is reported to occur in bipolar patients as a stable characteristic, i.e. a trait. Nevertheless, impulsivity has not been widely studied in depressed bipolar patients. We assessed impulsivity in depressed and euthymic bipolar and unipolar patients and healthy controls. We hypothesized that bipolar subjects would have higher levels of trait impulsivity than the comparison groups. METHODS: Twenty-four depressed bipolar, 24 depressed unipolar, 12 euthymic bipolar, and 10 euthymic unipolar patients, as well as 51 healthy subjects were evaluated with the Barratt Impulsiveness Scale (BIS). Analysis of covariance with age and sex as covariates was used to compare mean group differences. RESULTS: Depressed bipolar, euthymic bipolar, and depressed unipolar patients did not differ, and showed greater impulsivity than healthy controls on all of the BIS scales. Euthymic unipolar patients scored higher than healthy controls only on motor impulsivity. LIMITATIONS: Higher number of past substance abusers in the bipolar groups, and no control for anxiety and personality disorders, as well as small sample sizes, limit the reach of this study. CONCLUSIONS: This study replicates prior findings of stable trait impulsivity in bipolar disorder patients, and extends them, confirming that this trait can be demonstrated in depressed patients, as well as manic and euthymic ones. Trait impulsivity may be the result of repeated mood episodes or be present prior to their onset, either way it would influence the clinical presentation of bipolar disorder.