Stress manifests itself in our lives in a variety of ways, from financial concerns to health concerns, and leaves us irritable and grumpy. Over time, high levels of cortisol (the stress hormone), can begin to impact our physical, emotional and even mental health. However, it’s during times of stress we adopt an attitude of resiliency—but how exactly does the brain help us cope? Researchers have discovered our adaptive strategies to stressful situations originate from structural changes in the brain.
Published in the Journal of Neuroscience, the study found adult rats with disruptions in their social hierarchy produced far fewer neurons in the hippocampus—the part of the brain responsible for certain types of memory and stress regulation—but they reacted to the disruption by seeking the company of familiar rats. This shows how the decrease in production of new brain cells, known as "neurogenesis," has an active role in shaping the social behavior and adaptation in rats, and possibly humans.
"Even in the face of what appears to be a very disruptive situation, there was not a negative pathological response but a change that could be viewed as adaptive and beneficial," said Elizabeth Gould, senior author of the study and Princeton's Dorman T. Warren Professor of Psychology and department chair, in a statement.
Stress can excite brain cells to death. The cortisol released in stress travels into the brain and binds to the receptors inside many neurons in the cytoplasm. Through a series of reactions, this causes the neurons to admit more calcium through channels in their membrane. Theoretically, cortisol does help the brain to cope with life-threatening situations, but when these neurons are over-loaded with calcium, they tend to fire too frequently and die — literally being excited to death.
Ongoing stress also halts the production of new neurons in the hippocampus, and has the ability to affect the speed of connections between hippocampal cells. Interestingly, a single stressful event can destroy newly created neurons in the hippocampus. This is why the ability to be resilient is imperative to survive stressful situations.
In the study, the rats were placed into several groups consisting of four males and two females in a large enclosure known as a visible burrow system. The groups were monitored until the dominant rat in each one emerged and was identified. After a few days, the alpha rats of two communities were swapped, which called for a contest of who would be the next alpha rat in each group.
The rats from the disrupted hierarchies showed their preference for familiar rats six weeks after the shift, in which neurogenesis decreased by 50 percent. Any neurons generated during the time of instability would take four to six weeks to be incorporated into the hippocampus' circuitry, according to Maya Opendak, first author of the study, who received her Ph.D. in neuroscience from Princeton in 2015 and conducted the research as a graduate student.
"Indeed, sticking with a known partner rather than approaching a stranger may be beneficial in some circumstances,” said Opendak.
The researchers concluded organisms, including humans, are typically resilient in response to disruption and social instability.
"These results show that the reduction in new neurons is directly responsible for social behavior, something that hasn't been shown before," said Gould. However, the exact mechanism behind how lower neuron growth led to the behavior change is not yet clear.
It seems we’re biologically designed to handle social disruption and instability, which presumably, is what has kept us alive as a species for hundreds of thousands of years.
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