Chuck Bednar for redOrbit.com – @BednarChuck
The development of new neurons in adults appears to help the hippocampus better prepare for a variety of environmental factors, and the process is influenced in different ways by positive and negative experiences, researchers from Princeton University have discovered.
In research published Saturday in the journal Trends in Cognitive Sciences, Maya Opendak and Elizabeth Gould of the Princeton Neuroscience Institute explained that the birth of new neurons in the hippocampus (a region of the brain involved in memory and learning) can help people and animals adapt to their current circumstances in a complex, constantly changing world.
Fine-tuning the hippocampus
Opendak and Gould reviewed previous studies and other literature addressing the topic, and they reported that aversive experiences decrease neurogenesis, while rewarding ones tend to increase the production of new neurons. They added that those new neurons appear to be involved in most functions of the hippocampus, and may help optimize it anticipated circumstances.
As Opendak explained in a statement, “New neurons may serve as a means to fine-tune the hippocampus to the predicted environment. In particular, seeking out rewarding experiences or avoiding stressful experiences may help each individual optimize his or her own brain. However, more naturalistic experimental conditions may be a necessary step toward understanding the adaptive significance of neurons born in the adult brain.”
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It has become increasingly clear over the past few years that environmental factors have a profound influence on the adult brain in humans and several other types of mammals, the study authors explained. Stressful experiences such as social defeat, sleep deprivation and exposure to predator odors have been shown to decrease the number of new neurons in the hippocampus, while pleasant experiences such as mating and exercise increased neurogenesis.
The birth of new neurons during adulthood may come with important cognitive and behavioral consequences, they added. Stress-induced suppression of adult neurogenesis has been linked to impaired performance on spatial navigation learning, object memory and other cognitive tasks that depend on the hippocampus.
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Likewise, stressful experiences have been shown to increase the anxiety-type behaviors that are associated with the hippocampus. On the other hand, rewarding experiences have been linked to a reduction in anxiety-like behavior and improved performance on cognitive tasks involving the hippocampus, Opendak and Gould noted.
Improving the odds of survival
While most scientists agree that their daily actions change a person’s brain even in adulthood, there is no consensus on the adaptive significance of the development of new neurons. In their new study, the authors propose that stress-induced decreases in neurogenesis could improve the odds of survival by increasing anxiety and prioritizing safety and avoidant behavior by limiting the desire to explore and sacrificing some degree of cognitive performance.
“Because the past is often the best predictor of the future, a stress-modeled brain may facilitate adaptive responses to life in a stressful environment, whereas a reward-modeled brain may do the same but for life in a low-stress, high-reward environment,” explained Gould, a professor of psychology and neuroscience at Princeton University.
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When aversive experiences drastically outnumber rewarding ones in terms of quantity and intensity, however, a person’s system could reach a breaking point and produce maladaptive outcomes, she and Opendak added. For instance, repeated stress causes a prolonged reduction in neurogenesis, ultimately causing extreme anxiety and depression-like symptoms to emerge.
“Such a scenario could represent processes that are engaged under pathological conditions and may be somewhat akin to what humans experience when exposed to repeated traumatic stress,” said Opendak.
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