Brain imaging studies can reveal connections between brain regions that are associated with increased risk of suicide, a review of 131 papers has concluded. Whether the networks identified are the cause of higher suicide rates or the product of other factors that also make people more likely to take their own lives is less clear. Either way, the work could prove life-saving if it leads to improved identification of those most at risk.
Suicide is one of the largest causes of death worldwide, and one with a particularly large effect on life expectancy since it so often affects otherwise healthy people. Yet neuroscience has not treated it as a public health emergency.
"Imagine having a disease that we knew killed almost a million people a year, a quarter of them before the age of thirty, and yet we knew nothing about why some individuals are more vulnerable to this disease," co-lead author Dr Anne-Laura van Harmelen of the University of Cambridge said in a statement. "This is where we are with suicide. We know very little about what's happening in the brain, why there are sex differences, and what makes young people especially vulnerable to suicide."
Dr Lianne Schmaal from the University of Melbourne and van Harmelen noted in Molecular Psychiatry that the biggest risk factor for death by suicide is previous suicide attempts, particularly for adolescents. "If we can work out a way to identify those young people at greatest risk, then we will have a chance to step in and help them at this important stage in their lives," Schmaal said.
Using two decades of brain imaging research on more than 12,000 people, van Harmelen and Schmaal found two systems, or connections between brain regions, whose structure and function appear to be associated with a higher chance of attempting suicide, as well as increased suicidal thoughts. One of the networks connects areas of the brain involved in emotions. The authors propose that the differences in this region in people with a history of suicide attempts may hinder control of negative thoughts and depression. The other network links areas involved in decision making. Schmaal speculates the interaction between the two may make for a particularly risky mental state, although she says much more research is needed to confirm this.
Most of the studies the pair drew on had sample sizes too small to reveal much on their own, but by their powers combined proved revealing.
Schmaal stressed to IFLScience that we're a long way from being able to scan an individual's brain to determine their suicide risk. “All the studies are based on group averages,” she said. Moreover, almost none of the research looked at changes in brains over time, so we don't know if anything would be noticeable prior to suicidal thoughts, nor if anything changes when people's mental state improves.
“We do know from mental health studies in general that some features of the brain change when depression is treated successfully,” Schmaal noted. “That's a very hopeful message.” However, it's not clear how much it applies to what she has found.
Despite the value of the work they drew on, van Harmelen and Schmaal are disturbed about what is missing. Schmaal noted the amount of research was small compared to brain conditions like Alzheimer's or even schizophrenia, which affects far fewer people.
Moreover, sectors of the population known to have the highest risk of suicide today appear to be greatly underrepresented in the samples. “We know the least about the people we should study the most,” Schmaal told IFLScience. Hopefully, drawing attention to this deficit will prove to be the first step to fixing it.