A longitudinal study of adolescents from the Chicago metropolitan area found that in female, but not in male adolescents, higher exposure to violence was associated with more severe depression symptoms. In males, depression was associated with the expansion of the salience network of the brain and with increased connectivity of this network. The paper was published in Translational Psychiatry.
Violence exposure in this study was defined as experiencing, witnessing, or being repeatedly confronted with acts of interpersonal physical violence, such as being shoved, kicked, punched, or attacked with a weapon. It is a major risk factor for mental health problems, increasing the likelihood of all types of psychopathology.
Childhood adversities such as physical abuse and family violence account for a substantial proportion of psychiatric disorders that emerge during adolescence. This period is especially sensitive because key social and emotional brain systems are still developing. Exposure to violence during adolescence is associated with maladaptive emotion regulation strategies, such as rumination and emotional suppression, which contribute to rising rates of depression.
Although males are more likely to be exposed to or witness violence, females tend to show higher levels of depression during adolescence. Some evidence suggests that violence exposure places females at greater risk for internalizing problems (psychological difficulties directed inward), particularly depression and anxiety.
One explanation is that females may be more reactive to interpersonal stressors and show stronger physiological and neural responses to threat following violence exposure. Another proposed mechanism is perceived lack of control, as stressors experienced as uncontrollable are strongly linked to depressive outcomes.
Violence exposure may also alter brain systems involved in detecting and responding to threat, such as the salience network, making individuals more vigilant to potential danger. The salience network is a large functional neural network composed of multiple interconnected regions in the brain that detects and prioritizes behaviorally and emotionally important stimuli, helping the brain switch attention between internal thoughts and external demands.
Study author Ellyn R. Butler and her colleagues wanted to explore whether features of the salience network of the brain such as connectivity and expansion (the proportion of the cortex utilized by the network) may explain the association between exposure to violence and depression in adolescents. Study authors hypothesized that males experience more instances of violence than females and that depression symptoms will increase in individuals exposed to violence. They expected that this increase in depression symptoms after exposure to violence will be greater among females and that it will be accompanied by the expansion of the salience network.
Study participants were 220 adolescents between 14 and 18 years of age from the Chicago metropolitan area. Study authors intentionally prioritized adolescents from low-income neighborhoods for inclusion in the study. 141 of them were females. 38% were Black, and 30% were Hispanic. On average, they were exposed to 1.8 violent events in the past year.
Study participants provided study data twice – at the start of the study, and 2 years later. They completed an assessment of exposure to violence (a set of 7 questions about participants or their friends or family members being physically hurt, attacked, or killed) and assessments of depression and anxiety symptoms (the Revised Child Anxiety and Depression Scale).
Participants also underwent functional magnetic resonance imaging (fMRI) of their brains. The study authors used these fMRI data to derive information about connectivity and size of participants’ salience networks at both time points to control for baseline levels.
Results showed that female participants reporting greater exposure to violence tended to report more severe depressive symptoms. This association was not present in male participants. Salience network expansion or connectivity were not associated with exposure to violence in the past year.
However, greater expansion of the salience network and its greater connectivity were associated with more severe depressive symptoms in male participants. Study authors note that both of these associations remained after controlling for depression at the start of the study, indicating that exposures that impact males’ depression through the salience network may occur during middle adolescence.
“We demonstrated that salience network expansion and connectivity are positively associated with depression among males even after controlling for depression two years prior, highlighting that it is likely that males are experiencing some type of adversity that increases connectivity within the salience network, expansion of the salience network, and depression during this time period in early- to mid-adolescence. Therefore, future efforts to determine which exposures lead to depression during adolescence in males should focus on this developmental time frame,” the study authors concluded.
The study contributes to the scientific understanding of the neural underpinnings of depression. However, both depressive symptoms and exposure to violence in this study were self-reported, leaving room for reporting bias to have affected the results.
The paper, “Sex differences in response to violence: role of salience network expansion and connectivity on depression,” was authored by Ellyn R. Butler, Noelle I. Samia, Amanda F. Mejia, Damon D. Pham, Adam Pines, and Robin Nusslock.
