The biology of impulsivity and suicidality

Abnormalities of serotonergic and noradrenergic functioning have been associated with aggressive impulsivity, self-injurious behavior, and suicidal behavior. The role of dopamine and gamma-aminobutyric acid in human studies of these behaviors requires additional investigation. Most studies suggest that impulsive aggression is related to lower serotonergic activity, perhaps at the level of the amygdala or orbital prefrontal cortex. Some studies demonstrate that increasing norepinephrine correlates with more aggression. Self-injurious behavior also seems to be mediated by the neurotransmitter systems previously mentioned. For example, lower levels of serotonin and abnormalities in the dopaminergic system are related to self-injurious behavior in patients with borderline personality disorder or depression. Self-injurious behavior severity also seems to be influenced by neglect (severe isolation during rearing). Animal studies suggest that increasing the amount of isolation and an earlier onset of isolation increases the severity of self-injurious behavior. Suicidal behaviors and lethality of suicide attempts can also be linked to the abnormalities in neurotransmitter systems similar to those found in impulsive aggression or self-injurious behaviors, namely lowered serotonergic transmission and enhanced dopaminergic and noradrenergic function. Understanding the biologic triggers of impulsive aggression or self-injurious behaviors may eventually help early prediction and prevention of suicidal behaviors. Additional studies of live subjects and postmortem brains will assist in clarifying the neurobiology of suicidal behaviors that are common to many disorders but clinically are relevant to borderline personality disorder.