Background. Abnormal serotonergic neurotransmission has long been demonstrated in suicidal behavior. The dorsal and median raphe nuclei housing the main serotonergic cell bodies and the prefrontal cortex (PFC), particularly the ventral part innervated by the serotonergic system, have therefore been studied extensively in suicidal behavior research. However, only a few studies have described neuropsychological function impairment in suicidal patients. We investigated PFC-related neuropsychological function in patients with suicidal behavior, separating dorsolateral PFC (DLPFC)- and orbitofrontal cortex (OFC)-related functions.
Method. We compared 30 euthymic patients with suicidal behavior aged 18–65 years with 39 control subjects, for the following neuropsychological domains: global intellectual functioning, reward sensitivity, initiation, inhibition, and working memory. Patients and controls were compared by means of univariate and multivariate analyses, adjusting for age at interview, level of education and mood state at the time of evaluation. Trait impulsivity, measured with the Barratt Impulsivity Scale version 10 (BIS-10), was also included as a covariate in a subset of analyses.
Results. Multivariate comparisons demonstrated significant executive function deficits in patients with suicidal behavior. In particular, we observed impairment in visuospatial conceptualization (p<0·0001), spatial working memory (p=0·001), inhibition (Hayling B–A, p=0·04; go anticipations, p=0·01) and visual attention (or reading fluency) (p=0·002). Similar results were obtained following adjustment for motor impulsivity as a covariate, except for spatial working memory.
Conclusions. These deficits are consistent with prefrontal dysfunction in patients with suicidal behavior. Differentiation between DLPFC- and OFC-related neuropsychological functions showed no specific dysfunction of the orbitofrontal region in patients with suicidal behavior in our sample.
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