A region of the brain called the hippocampus is known for its role in memory formation. Scientists at Yerkes National Primate Research Center, Emory University are learning more about another facet of hippocampal function: its importance in the regulation and expression of emotions, particularly during early development.
Using a nonhuman primate model, their findings provide insight into the mechanisms of human psychiatric disorders associated with emotion dysregulation, such as PTSD (post-traumatic stress disorder) and schizophrenia. The results were published online recently by the journal Psychoneuroendocrinology.
“Our findings demonstrate that damage to the hippocampus early in life leads to increased anxiety-like behaviors in response to an unfamiliar human,” says research associate Jessica Raper, PhD, first author of the paper. “However, despite heightened anxious behavior, cortisol responses to the social stress were dampened in adulthood.”
The hormone cortisol modulates metabolism, the immune system and brain function in response to stress. Reduced hippocampal volume and lower cortisol response to stressors have been demonstrated as features of and risk factors for PTSD, Raper says. Also, the dampened daily rhythms of cortisol seen in the nonhuman primates with hippocampal damage resemble those reported in first-episode schizophrenia patients.
Follow-up studies could involve temporary interference with hippocampus function using targeted genetic techniques, she says.
These emotional and neuroendocrine changes were similar to those reported in subjects who acquired damage to the hippocampus in adulthood, suggesting little functional compensation occurs during development. The changes also resemble those found in human patients with hippocampal damage.
“Overall, our results suggest hippocampal dysfunction results in behavioral and hormonal features seen in some neuropsychiatric disorders, demonstrating the key role the hippocampus plays in the clinical symptoms of patients,” Raper says.
The study was a continuation of a larger project by Jocelyne Bachevalier, PhD, at Yerkes National Primate Research Center, which studied how hippocampal damage within the first month of life affect cognitive development and memory. Yerkes researchers Mark Wilson, PhD, and Mar Sanchez, PhD, and Christa Payne, PhD, in the Department of Pediatrics at Emory University, were part of the collaboration.
The research was supported by the National Institute of Mental Health (MH58846, MH732525), the National Institute for Child Health and Development (HD35471), the National Science Foundation (Center for Behavioral Neuroscience: IBN 9876754) and the Office of Research Infrastructure Programs (Primate centers: P51OD11132).