You’ve had a hard day at work or at home or both and you’re feeling “stressed out.” Now you have even more reason to worry!
It turns out that repeated exposure to stress causes changes in the brain that can set the stage for a multitude of mental and physical health problems, from depression to heart disease.
Now a recent paper in Psychological Review, explains why. Drawing on research across multiple fields, Barbara Ganzel, neuroscientist in the Department of Human Development, and her colleagues Pamela Morris from New York University and Elaine Wethington in the Department of Human Development developed a new model of the stress process and how it affects the brain and body over time.
“We needed a framework that would integrate the emerging insights from neuroscience with research in other fields so we could really understand the interplay between stress exposure, regulation of body processes and health outcomes,” said Ganzel.
Here's how it works.
Your body’s stress response kicks in when you perceive a threat. Your heart beats faster and your blood pressure increases along with other changes which prepare your brain and body for action. This is a remarkable survival system for responding to danger. But most daily stressors are not life-threatening. They are more individualized. We perceive and respond to a situation in the context of our current environment and health, influenced by our past environment and health, upon the foundation of our genetics.
A set of brain regions which includes the amygdala and basal ganglia is the hub of our response to threats and rewards. Processing of such emotional stimuli is regulated by neurotransmitters and neurohormones within these regions.
These core emotional regions of the brain work in conjunction with other brain areas to interpret the situation and generate a behavioral response. Together, the core emotional regions of the brain function as the first responders to threat. This central response then drives all of the other stress-related changes in the body.
In response to a stressor, neurochemical signals generated by the core emotional regions of the brain activate the hypothalamus in the brain, pituitary gland at the bottom of the brain, and the adrenal glands. The adrenal glands then produce cortisol and adrenaline which have global preparatory and modulating effects on the rest of the body’s systems such as the immune system, cardiovascular system and digestion.
An individual’s response to stress is influenced by their environment. There are potential risks that may confound and resources that may help the individual undergoing the stressor. For instance, research has shown that social support can buffer the impact of negative events on mental and physical health. Intriguingly, results from fMRI studies indicate that the availability of social support can prevent or reduce the brain’s initial emotional reactivity to stress, though more research needs to be done to fully understand this relationship.
Over time the process of responding to stress causes wear and tear on the brain and body. While minor stressors may function as healthy challenges that leave little or no negative effects, larger stressors make greater demands. Under chronic or repeated stress, the long term physiological costs of the sustained accommodation to stress continue to accumulate.
In the authors’ model, mental health is affected by the stress response process in the brain and physical health is affected by the stress response process in the body. And, of course, each affects the other. Accumulated wear and tear and the associated mental and physical health outcomes feed into the individual’s environmental risks. Importantly, accumulated wear and tear also directly affects the individual’s mental and physical capacity to respond to a current stressor.
An example is blood pressure, which increases in response to perceived danger. Repeated exposure can result an upward regulation of the blood pressure set point to more permanently accommodate the stressful environment. Chronic high blood pressure, in turn, can lead to a host of other health problems which feed back into the dynamics of an individual’s neural response to stress.
Genetics and gene-environment interactions, importantly, enter into the model. Individual differences in genetics affect the biology of the current stress response as well as the accumulation of wear and tear. Individual differences modify an individual’s first and subsequent responses to stressors in the environment. One example is the natural genetic variation in a serotonin transporter gene. Carriers of one version are more sensitive to negative stimuli. Under stressful conditions such individuals have an increased risk for depression.
Research has identified multiple indicators of accumulated stress load on the body. Chronic high blood pressure is but one example. Emerging evidence from neuroimaging studies confirms that there are long-term effects of stress on the healthy human brain as well. Since the emotional systems of the brain are the focal point for response to stress, indicators of wear and tear would be expected to show up as structural, functional or neurochemical shifts in these brain systems. These, in turn, translate into alterations in behavior such as increased startle response or anxiety. Ganzel found just such effects in her earlier research on 9/11 survivors in which adults closer to the disaster had smaller more stress-reactive amygdalae.
”In our whole group, amygdale reactivity and amygdale gray matter volume was related to lifetime trauma exposure and predicted anxiety and symptoms of post traumatic stress syndrome,” said Ganzel. There is evidence from a broad set of research findings that severe, chronic or repeated stress plays a role in a multitude of health issues such as anxiety, depression, and suppressed immunity.”
This model provides a framework for better understanding those links and designing new approaches to medical and social problems – from heart disease to child abuse.
Reference
Ganzel, B.L., Morris, P.A. and Wethington, E. (2010). Allostasis and the human brain: Integrating models of stress from the social and life sciences. Psychological Review, 117(1), 134-174.