Predators can inspire fear that causes long-lasting changes to the brains and behaviors of wild animals, helping them remember and avoid such life-threatening events in the future.
Researchers describe this as an "animal model" of post-traumatic stress disorder (PTSD) that suggests the condition may not be a maladaptive dysfunction, but rather a phenomenon that occurs in nature to enhance survival against perceived threats. Retaining a powerful and long-term memory of a life-threatening encounter is “clearly evolutionarily beneficial” if it helps an individual avoid such events in the future, note the researchers.
“These results have important implications for biomedical researchers, mental health clinicians, and ecologists,” said study author Liana Zanette in a statement. “Our findings support both the notion that PTSD is not unnatural, and that long-lasting effects of predator-induced fear with likely effects on fecundity and survival, are the norm in nature.”
To test how wild animals are affected by life-threatening events, researchers at Western University in Canada exposed wild-caught black-capped chickadees to audio recordings of predators over the course of two days. A week after the experiment, birds who had been exposed to threatening sounds that signaled predator threats had a heightened sensitivity to danger, indicating a memory of fear. The researchers further measured changes in the amygdala and hippocampus of the brain, finding that physical changes occur and can last for extended periods of time.
Animals exposed to the threats of predators experienced changes to the neural circuitry in their brains, which were longer-lasting than an immediate “fight or flight” response. In fact, behavioral changes were observed up to a week later in chickadees exposed to natural environmental and social conditions.
“Our results demonstrate enduring effects on the brain and behavior, meeting the criteria to be considered an animal model of PTSD,” wrote the authors in Scientific Reports, highlighting the fact that these observations were seen in wild birds.
Life-threatening events can have enduring effects on the brain and behavior, note the researchers. Some scientists believe that PTSD could be an inherited quality in humans that prioritizes survival over quality of life, but in order to determine a medical treatment in humans, science first aims to determine, diagnose, and develop a treatment for ailments in animals in the laboratory setting.
Previous research by Zanette shows that scared songbirds are less able to care for their young, which, when considered in conjunction with the current study, suggests being exposed to stressful situations could impair parental behaviors for a prolonged period of time, having negative repercussions for offspring in the long term. Altogether, the researchers note their findings could help inform a better understanding of the intersection between ecology and environmental experiences and the effects they can have on the brain.