Limitations in our capacity to predict the occurrence of suicidal behavior constitute a major problem in the prevention of suicide. Due to their extremely limited predictive value, ratings scales and clinical measures are not available for practical use. This is an area in which neuroscience can be expected to contribute substantially via the identification of biomarkers using genetic and brain imaging techniques. Recent studies using genetic approachessuggest the existence of specific biomarkers that can be detected in the blood. In addition, findings from neuroimaging and neuropsychological studies indicate functional impairments with increasing specificity in association with suicidal behavior. Biomarkers can be expected to contribute substantially to the devlopment of accurate prediction in the context of personalized medicine.

The core question in suicide prevention is: why does a person in a particular situation take their own life, while another person in the same situation would react in a different way? This chapter investigates to what extent and in which way neurocognitive studies may contribute to finding an answer to this question. The term 'neurocognitive' refers to the study of the relationship between the brain and behavior by utilizing specialized tests that have been designed to evaluate a wide variety of behavioral, cognitive and emotional domains. Thus, neurocognitive studies contribute to understanding how behavioral decisions following exposure to particular environmental stimuli relate to changes in brain functions. Such studies offer a great opportunity to measure and quantify cognitive functions, emotional states and behavioral repertoires through standardized questionnaires and testing. From such neurocognitive data, inferences are made regarding brain function and the localization of brain dysfunctions based on patterns of cognitive strengths and weaknesses. As conclusions from neuropsychological assessments are necessarily inferential, findings from neuropsychological investigations are commonly combined with those from neuroimaging (see next chapter) in order to fully understand the relationship between behavioral phenomena and changes in brain functions.

Results from a range of studies using diverse designs and both postmortem and in-vivo techniques show impairments in the serotonin neurotransmitter system and the hypothalamic–pituitary–adrenal (HPA) axis stress-response system in the vulnerability to suicidal behaviour. The involvement of serotonin in the development of suicidal behavior is well known since the 1970s when low levels of serotonin metabolites in the cerebrospinal fluid of suicide attempters were demonstrated. This involvement has been confirmed in numerous subsequent postmortem and in-vivo neuroimaging studies. For example, molecular imaging studies have localized lower binding to the serotonin transporter in areas of the brain, such as the ventromedial prefrontal cortex, which are known to be involved in decision-making processes. Serotonergic impairments may also manifest as impaired cognitive control of mood, pessimism, impaired problem solving, increased reactivity to negative social signs, excessive emotional pain, and suicidal ideation, leading to suicidal behavior.