Researchers at the Icahn School of Medicine at Mount Sinai have identified a previously overlooked brain circuit that helps explain how prior adversity can make the brain more reactive to future stress.
The study, published September 30 in Nature [https://doi.org/10.1038/s41586-026-11075-5] and conducted in mice, identifies a small, deep brain structure called the anterior hypothalamic nucleus (AHN) as a critical hub that scales the brain’s response to threatening events. The research team found that dialing its activity up or down directly altered how strongly the animals responded to stress.
“Why do some people develop debilitating mental health conditions in response to stress while others do not? One known risk factor for heightened stress sensitivity is a history of prior stress, such as early childhood adversity or adult traumatic stress. However, at a biological level, we still do not fully understand why this is the case,” says Zachary Pennington, PhD, lead author of the paper, who conducted the research as a postdoctoral fellow in the Cai Lab at Mount Sinai and is now an Assistant Professor of Psychology and a member of the Djavad Mowafaghian Centre for Brain Health at the University of British Columbia.
“Here, we identified a new pathway in the brains of mice that contributes to heightened stress sensitivity following a prior stressful experience,” Dr. Pennington says. “Although we still need to determine the contribution of this pathway to stress sensitivity in humans, we are excited by the prospect of finding ways to target this pathway to alleviate symptoms in conditions like post-traumatic stress disorder (PTSD).”
It has long been known that people who have experienced early-life adversity or prior psychological trauma are more likely to develop conditions such as PTSD, anxiety, and depression after a subsequent stressful event. Yet the underlying brain circuitry driving this heightened vulnerability has remained poorly understood. Most previous research has focused on a small set of regions, including the amygdala, prefrontal cortex, and hippocampus.
“We usually look for the effects of stress in familiar brain regions such as the amygdala, hippocampus, and prefrontal cortex. But Zach wanted to know what we might be missing, so he took an unbiased approach and looked across the entire brain,” says Denise Cai, PhD, Associate Professor of Neuroscience, Co-Director of the Integrative Systems Neuroscience and Computation Center at the Icahn School of Medicine, and senior author of the study. “The anterior hypothalamus was a genuine surprise. This region has traditionally been studied for regulating basic bodily functions and defensive behaviors. We did not expect it to carry the history of prior stress and help determine how strongly the brain responds to the next stressful event.”
Rather than focusing on brain regions already associated with stress, the Mount Sinai team searched across the entire brain. This unbiased approach led them to the AHN, a small region not traditionally considered a major focus of stress research. The researchers then used miniature microscopes to watch individual neurons in the AHN as freely moving mice encountered experiences of different intensities. They found that the circuit tracked how negative an experience was and became more sensitive in animals with a history of prior stress. The AHN also became more strongly coordinated with a broader network of threat-related regions, including the amygdala, hippocampus, and medial prefrontal cortex.
The researchers found the AHN was not simply registering stress; rather, it was controlling the magnitude of the response. Increasing AHN activity intensified defensive responses, while decreasing its activity reduced them. Most strikingly, silencing the pathway carrying information from the amygdala to the AHN prevented prior stress from amplifying the animals’ response to a later threat. Together, the findings suggest that this circuit helps the brain use the past to set the intensity of its response to what happens next.
“What surprised me most was how much influence such a small circuit could have. By turning its activity up or down, we could increase or decrease how strongly the animals responded to stress. It acted almost like a volume knob, amplifying or dampening the impact of a threatening experience,” says Dr. Cai.
“If we want more precise treatments for stress-related disorders, we cannot limit ourselves to the brain regions we already know,” Dr. Cai adds. “Unbiased discovery can reveal entirely new circuits and new places to intervene. This study gives us an unexpected candidate for understanding how trauma and adversity leave lasting marks on the brain.”
“Stress can have profound negative impacts on our mental and physical health, so understanding the biology of stress sensitivity could provide new ways to intervene in these pathologies,” says Dr. Pennington. “We all experience stress on a near-daily basis, and sometimes we are better equipped to handle it than others. Some days we let a stressor roll off our backs, while other times our days are consumed by it. Understanding this fluctuation is fundamental to a huge part of our lives.”
About the Icahn School of Medicine at Mount Sinai
The Icahn School of Medicine at Mount Sinai is internationally renowned for its outstanding research, educational, and clinical care programs. It is the sole academic partner for the seven member hospitals* of the Mount Sinai Health System, one of the largest academic health systems in the United States, providing care to New York City’s large and diverse patient population.
The Icahn School of Medicine at Mount Sinai offers highly competitive MD, PhD, MD-PhD, and master’s degree programs, with enrollment of more than 1,200 students. It has the largest graduate medical education program in the country, with more than 2,700 clinical residents and fellows training throughout the Health System. The Graduate School of Biomedical Sciences offers 12 degree-granting programs, conducts innovative basic and translational research, and trains more than 470 postdoctoral research fellows.
Ranked 11th nationwide in National Institutes of Health (NIH) funding, the Icahn School of Medicine at Mount Sinai is among the 90th percentile of U.S. private medical schools in Sponsored Programs Direct Expenditures per Principal Investigator, according to the Association of American Medical Colleges. More than 6,900 scientists, educators, and clinicians work within and across dozens of academic departments and multidisciplinary institutes with an emphasis on translational research and therapeutics. Through Mount Sinai Innovation Partners (MSIP), the Health System facilitates the real-world application and commercialization of medical breakthroughs made at Mount Sinai.
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* Mount Sinai Health System member hospitals: The Mount Sinai Hospital; Mount Sinai Brooklyn; Mount Sinai Morningside; Mount Sinai Queens; Mount Sinai South Nassau; Mount Sinai West; and New York Eye and Ear Infirmary of Mount Sinai.
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Nature
Experimental study
Animals
An amygdala to anterior hypothalamic circuit gates stress sensitivity
30-Sep-2026