Fear and trauma are useful for animals — can we learn from them how to live without it?
PTSD may be partly rooted in our evolutionary past as animals constantly threatened by predators
Researchers studying the way fear and trauma in animals leads to the inscription of powerful memories think this might give some insight into the roots of trauma-related psychological disorders in humans.
According to a study published in the journal Scientific Reports, wild animals' exposure to predators and the fear it instills in them can result in animals developing debilitating symptoms very much like we see in people experiencing Post Traumatic Stress Disorder (PTSD).
Liana Zanette, a biology professor from the University of Western Ontario, said in conversation with Quirks & Quarks host Bob McDonald that she's discovered that animals that were exposed to predator cues retained a hypersensitivity to predator threat. That extra sensitivity was detectable in their behaviour, but also in different levels of activity in fear-related areas of their brains.
One week after Zanette exposed chickadees to a predator call, those wild birds became hypervigilant to potential danger in their environment and showed an enduring imprint in the birds' neural networks associated with fear.
For animals that face life and death situations daily, Zanette said these responses to fear make "perfect evolutionary sense."
Where it might stop making sense is in humans suffering from PTSD. A frequent manifestation of PTSD is that long after a person is removed from the life threatening danger, the debilitating fear persists, severely impacting the quality of their life.
"Because fear memories are so powerful — and are so powerful for a very good evolutionary reason — it is difficult to alter them," said Zanette.
Trickle down effects of fear on wild animals
Elevated fear responses in animals might help them survive, but there is a cost. Fear of predators can severely impact the prey's ability to feed and successfully produce offspring, which can ultimately affect entire populations and ecosystems.
Zanette said wild animals in risky environments can never really let down their guard unless they want to become food for some other predator. "But the cost of this means that you're going to forgo many meals as a result."
In another study, she also discovered that when birds thought predators were around, they produced 40 per cent fewer offspring over the breeding season.
"If a parent is fearful during that time, is hypersensitive to danger so it's looking for predators (...) that means it's not looking for food to feed those offspring," she said.
Fear can affect population numbers, but if prey aren't eating themselves, then the prey's preferred meal choice then gets a chance to proliferate, leading to a change in the ecosystem.
Inheritance of fear becomes biological
The traumatic effects of fear and stress can have repercussions that can have other kinds of impacts on offspring.
Brian Dias, an assistant professor of psychiatry at Emory University School of Medicine explained that studies of descendants of people who've suffered malnutrition with famines, as well as descendents of Holocaust survivors, suggest "there are legacies of stress that echo across generations."
In previous studies with lab rodents, he discovered a kind of 'memory' of fear can be passed down through generations in ways unrelated to ordinary learning. Fear can be inscribed in the cells through a biological mechanism.
The mechanism involves small non-coding RNA that he says "act like puppeteers" to orchestrate how genes are expressed.
"We're talking about a phenomenon called epigenetics," said Dias. "These RNA are what are allowing the genes to be either read a lot or to actually not be read at all."
Dias has observed changes in these RNA being passed down through sperm so that mice inherit the fear responses of their fathers.
A reversal of intergenerational effects of fear
Just as you can turn on epigenetic effects when a fear is learned, Dias has more recently discovered he can also turn off those effects. These findings were recently published in the journal Biological Psychiatry.
"What we do is we administer what is called 'extinction learning,' which is very akin to cognitive behavioural therapy in humans," said Dias.
Mice previously trained to associate foot shocks with a certain smell are, by repetition, taught to develop a new, more benign association to the same smell.
"What we now find is that the offspring are no longer are sensitive to that smell. Their brains [are] no longer devote more real estate to its processing that smell. And the sperm of the animals who been made unafraid to that particular smell, those imprints also go away."
He says these findings should give us optimism to hope that the effects of intergenerational trauma can be reversed.