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Post traumatic stress disorder (PTSD) affects eight per cent of adults in the United States. That means eight million Americans suffer from PTSD annually. Women are more likely to suffer from PTSD than men. While 10 per cent of women develop PTSD at some point in their lives, four per cent of men will experience PTSD.

One of the responses to PTSD is anger as well as depression, chronic pain, sleep problems, substance misuse, suicide, and grief. A new study published in the Journal of Neuroscience examined the link between traumatic stress and aggression.

“Our study is about how experience influences aggression, in particular attack experience and traumatic stress,” lead author Dr. Zheng Li told us. “We were hoping to identify the brain circuits and synapses that are responsible for the effect of experience on attack behavior.”

PTSD is often most associated with veterans. Between 11 and 20 per cent of veterans of Operations Iraqi Freedom and Enduring Freedom have PTSD. PTSD also affects children and adolescents. Three to 14 per cent of girls and one to six per cent of boys in the U.S. suffer from PTSD. The events that cause PTSD in children and teens are neglect (65 per cent), physical abuse (18 per cent), sexual abuse (10 per cent), and psychological abuse (7 per cent).

Previous studies have suggested that PTSD is linked with increased neural activity in the amygdala. Therefore, the current study’s researchers hypothesized that prior attack experience and traumatic stress provokes lasting attack behavior through the strengthening of synapses within an amygdala circuit.

“Our lab is interested in the role of synaptic plasticity in experience-dependent modification of behaviors and the synaptic mechanism underlying psychiatric disorders,” Dr. Li told us. “PTSD is a devastating condition that has a lifetime prevalence of 6.8 per cent. Recurrent and excessive aggression is a symptom of PTSD and can cause serious consequences to the individual and society. There is no specific and effective treatment for it. Understanding the neural basis of the aggression symptom of PTSD can facilitate the development of new treatment strategies. We, therefore, choose this study topic.”

Researchers tested their hypothesis that aggressive encounters and traumatic stress increase aggression through the strengthening of amygdala pathways by measuring synaptic strength in these pathways before and after an attack or traumatic stress; and by altering synaptic strength within these pathways to suppress the subsequent increases in aggression.

“We observed that attack and traumatic experience increases aggression,” Dr. Li told us. “We also found that these experiences increase synaptic strength within the medial amygdala (MeA) to the ventomedial hypothalamus (VMH) and the bed nucleus of the stria terminalis (BNST) pathways.”

Dr. Li’s team also learned that decreasing synaptic strength within these pathways suppresses the heightened aggression induced by attack and traumatic experience and that increasing synaptic strength within these pathways could promote aggression independent of prior attack or traumatic experience.

“We were surprised to discover that two of the amygdala pathways we investigated regulated specific types of attack behavior, namely that one pathway promotes attack frequency while the other promotes attack duration,” Dr. Li told us. “The results of our study indicate the MeA-VmH and MeA-BNST pathway and synaptic potentiation can be potentially targeted in the treatment of excessive aggression associated with PTSD.”

Dr. Li believes the incidence of violence in today’s society demonstrates the great need to investigate the neural mechanism of aggression and especially how experience can shape violent aggression.

“As such,” notes Dr. Li, “we believe our study is a timely addition to the field of aggression research.”