the neurobiology of suicide

by Mary Taglieri, GCSOM, MBS 2019
Mentor: Dr. Brian Piper, PhD


Suicide is a global epidemic, and quickly rising as a leading cause of death for individuals aged 15-29. It is estimated that suicide is responsible for 800,000 deaths a year, with 16 million attempts occurring each year. It is vital that the medical and mental health fields are equipped with the best knowledge on how to address this crisis.

I have volunteered in the mental health field for three years as a Crisis Counselor, helping to provide support for individuals in crisis and provide them with coping skills, resources, and the confidence to overcome their personal battles. Through this, I have spoken with over 2,700 individuals, the plurality of whom struggle with suicidal ideation. It has been an honor to be trusted with their most vulnerable thoughts and emotions, and I dedicate this project to those who are fighting suicidal thoughts.

Suicidal behavior is defined by Brent as, “the tendency to act on suicidal thoughts.” This means that while clinically defined suicidal behavior requires suicidal ideation, suicidal behavior does not include ideation itself without a behavioral manifestation. As suicidal ideation is not considered to be on the same spectrum as attempted suicide and completed suicide, it was therefore not screened for as a confounding variable in research studies the way other mood disorders and psychiatric diagnoses were.

The stress-diathesis model is a commonly discussed hypothesis that states that an individual has a biological predisposition to suicide (the diathesis) but does not exhibit suicidal behavior until an environmental trigger (the stress) occurs. Therefore, much research on the neurobiology and physiology of suicide looks at the biological differences between an individual who exhibits suicidal behavior and an individual who does not exhibit suicidal behavior, but who are both under similar environmental stresses. Some common factors researchers look at when trying to compare similar backgrounds include socioeconomic level, family stability, and profession.

Suicidal behavior can be further broken down into categories based on its violence and impulsivity; and attempted suicide can further be broken down based on the lethality of the means. It is generally accepted that violent suicide is a more severe version of suicidal behavior than of nonviolent suicide, and that more lethal suicide attempts are a more severe version of suicidal behavior than a less lethal suicide attempt.

The presence or lack of impulsivity is interesting, as one isn’t considered to be more severe than the other. Rather, there are different risk factors for each category, with Brent proposing a potential link between familial transmission of impulsive aggression and impulsive suicidal behavior.

Suicide has been linked to dysfunctions in the serotonin, noradrenergic, and dopaminergic systems. The serotonin system has been the most studied in relationship to suicidal behavior, and generally contributes to feelings of well-being and happiness. The noradrenergic system is responsible for the stress response and releases both adrenaline and cortisol (the stress hormones) during times of fight-or-flight. The dopamine system is responsible for the reward response, that is connecting a feeling of satisfaction with an action or object. More recent investigations have looked at connecting the immune system with suicidal behavior, and this system is primarily responsible for protecting the body against external and internal threats.

It has been observed that suicidal behavior is related to lower levels of serotonin in the spinal fluid, and research has provided evidence supporting the hypothesis that individuals exhibiting suicidal behavior have less serotonin than individuals without suicidal behavior. This is believed to be caused by a decrease in the amount of serotonin being produced.

It has also been demonstrated that suicidal behavior is connected to lower cortisol levels both in baseline levels and in response to stress. This supports the stress-diathesis model in providing evidence for a different response to stress in suicidal individuals compared to non-suicidal individuals.

While not as well studied as the serotonergic and noradrenergic systems, it has been seen that decreased dopamine levels can also be connected with suicidal behavior.

In one interesting study, researchers found high levels of antibodies for dopamine in individuals exhibiting suicidal behavior, meaning that their immune systems were attacking and decreasing the levels of dopamine. This could be a connection between suicide and an autoimmune disorder. Furthermore, when researchers began looking at the immune system in individuals with suicidal behavior, they found increased levels of inflammatory chemicals in the blood, showing an overactive immune system.

In conclusion, suicide is a complex phenomenon that has both biological and environmental risk factors. However, a greater understanding of these biological manifestations has led to the development of anti-depressants that can act to increase the amounts of serotonin, norepinephrine, and dopamine in the nervous system and potentially help to prevent suicidal behavior.