Suicide can be viewed as an escape from unendurable punishment at the cost of any future rewards. Could faulty estimation of these outcomes predispose to suicidal behavior? In behavioral studies, many of those who have attempted suicide misestimate expected rewards on gambling and probabilistic learning tasks.
To describe the neural circuit abnormalities that underlie disadvantageous choices in people at risk for suicide and to relate these abnormalities to impulsivity, which is one of the components of vulnerability to suicide.
Case-control functional magnetic resonance imaging study of reward learning using a reinforcement learning model.
University hospital and outpatient clinic.
Fifty-three participants 60 years or older, including 15 depressed patients who had attempted suicide, 18 depressed patients who had never attempted suicide (depressed control subjects), and 20 psychiatrically healthy controls.
Main Outcomes and Measures
Components of the cortical blood oxygenation level–dependent response tracking expected and unpredicted rewards.
Depressed elderly participants displayed 2 distinct disruptions of control over reward-guided behavior. First, impulsivity and a history of suicide attempts (particularly poorly planned ones) were associated with a weakened expected reward signal in the paralimbic cortex, which in turn predicted the behavioral insensitivity to contingency change. Second, depression was associated with disrupted corticostriatothalamic encoding of unpredicted rewards, which in turn predicted the behavioral oversensitivity to punishment. These results were robust to the effects of possible brain damage from suicide attempts, depressive severity, co-occurring substance use and anxiety disorders, antidepressant and anticholinergic exposure, lifetime exposure to electroconvulsive therapy, vascular illness, and incipient dementia.
Conclusions and Relevance
Altered paralimbic reward signals and impulsivity and/or carelessness may facilitate unplanned suicidal acts. This pattern, also seen in gambling and cocaine use, may reflect a primary deficit in the paralimbic cortex or in its mesolimbic input. The overreactivity to punishment in depression may be caused in part by a disruption of appetitive learning in the corticostriatothalamic circuits.