PSY 340 Brain and Behavior
Class 29: Stress and Health
I. Stress and the Autonomic Nervous System
- During the 1950s, the Czech-Canadian physiologist, Hans Seyle (1907-1982), developed the first important theories regarding the relationship between stress and health.
- Stress = the response of the body to any demand put upon it. Note that the demands can be not only physical (e.g., the effects of weather, cold, heat, etc.), but also psychological.
- Types of stress: pleasant (e.g., getting married) and unpleasant (e.g., death of a loved one, financial difficulties)
- General Adaptation Syndrome: A generalized response by the body to continued stress which comes in three stages
- Stage 1: Alarm = sympathetic nervous system readies body for brief emergency
- Stage 2: Resistance = adrenal gland secrete cortisol & other hormones to promote alertness, fight infections, and heal wounds
- Stage 3: Exhaustion = after prolonged stress, body becomes tired, inactive, and vulnerable to infections, etc.
II. Stress, the HPA Axis, & the Immune System
- Stress activates two body systems: the (1) autonomic nervous system and (2) the HPA Axis (hypothalamus-pituitary gland-adrenal cortex)|
- The hypothalamus sends CRF (corticotropin releasing factor) to the pituitary gland which secretes ACTH (adrenocorticotropic hormone) into the bloodstream which, when it reaches the adrenal cortex, stimulates the production of cortisol. When operating normally, elevated levels of cortisol serve in a negative feedback loop to suppress the further production of CRF and ACTH. Thus, cortisol inhibits its own secretion. The hippocampus appears to be a major neural structure to inhibit the HPA axis; hence, damage to the hippocampus would be expected to upset the normal functioning of the axis.
- Cortisol (aka hydrocordisone) mobilizes body's energies by increasing blood sugar and metabolism rate (while lowering rate of protein synthesis). In the short-term this is helpful, but in the long-term, this is damaging to the body.
- Chronic stress in which cortisol is elevated for long periods of time has been associated with a range of health problems including type 2 diabetes and metabolic syndrome (increased blood pressure, high blood sugar, excess body fat around the waist, and abnormal levels of cholesterol or triglycerides in the blood). In addition to diabetes, metabolic syndrome increases the risk of heart disease and stroke.
- Cortisol & the Brain: Negative Effects (not in book)
- In addition to the effects on blood sugar, protein synthesis, and metabolism rate, the cortisol molecule easily crosses the blood-brain barrier and affects the central nervous system, particularly areas having to do with cognition (Ouanes & Popp, 2019).
- Functional Effects.
- Research has consistently found that high levels of circulating cortisol among otherwise healthy older adults without dementia is associated with poorer episodic memory.
- Structural Effects.
- Among the elderly, high cortisol levels are associated with a smaller hippocampus and greater memory problems.
- Other studies of healthy middle-age adults find high cortisol levels associated with decreased volume of various brain areas involved in cognition including decreased total brain volume (especially decreased occipital & frontal grey matter) as well as microstructural changes in the corpus callosum and other structures [Oaunes & Popp, 2019, p. 3; Echouffo-Tcheugui, J. B. et al (2018)].
- Alzheimer's Disease (AD)
- The impact of stress in elevating the H-P-A Axis into chronic over-activity has been hypothesized to be a risk for the development of AD or speeding up the neural deterioration of patients with AD.
- Among individuals with varying levels of Alzheimer's disease, high levels of cortisol are associated with both lower overall brain volume as measured by MRI and lower levels of brain metabolism as measured by PET scanning ("hypometabolism"; Wirth et al., 2019). "Taken together, our findings are convergent with the idea that HPA axis activation may be a vigorous mechanism that accelerates AD pathogenesis. The study shows detrimental relationships between stress hormone levels and brain integrity within regions sensitive to AD pathology across the AD spectrum" (Wirth et al., 2019, p. 23)
- Other researchers have found that high cortisol levels are associated with a faster decline in AD patients while cortisol levels are an accurate biomarker for deterioration from mild cognitive impairment to full AD (Oaunes & Popp, 2019).
Effects of Stress on the Immune System
Cytokines: When we are sick, T-cells (a type of immune system cell in our blood) release chemicals called cytokines (e.g., interleukin-1). These combat infections and also communicate with the brain to promote appropriate nervous system responses. As we saw in an earlier chapter, cytokines stimulate receptors of the vagus nerve which, in turn, relays messages to the hypothalamus and hippocampus to release cytokines within the brain, too.
- These prompt the development of a fever
- Increased sleep, decreased muscle activity, and decreased sex drive conserve energy
- Decreased appetite might be helpful by curbing the need to work to provide food
Strong, inescapable, and temporary stresses trigger similar responses to those caused by an illness: fever, sleepiness, decreased appetite & sex drive
Brief stress causes SNS arousal and HPA Axis arousal: in the short run, these strengthen the body.
Long-term or chronic stress, anger, or anxiety leads to harm of the body, e.g.,
- Prolonged cortisol release seems to limit the synthesis of immune system cell proteins, e.g., people living near the Three-Mile Island nuclear plant accident (1979) over the subsequent year had decreased immune system cells
- Antarctic researchers over 9 months of cold, dark, and isolation show reduced T-cells functions (ca. 50% of normal).
- Exposure to common cold viruses does not lead to increased illness for those subject to less than a month of stress; individuals with 4 or more weeks of stress are more likely to become sick.
- Recent research of children who had been subjected to severe child maltreatment by their parents by the age of 3 demonstrated significant negative alterations in the overall connectivity patterns in the development of the white matter of their brains (as compared to matched control children; Puetz et al., 2017). The researchers note that such findings are in line with research showing that high levels of HPA axis activation and chronic exposure to cortisol affects neural development in children.
Echouffo-Tcheugui, J. B. et al (2018) Circulating cortisol and cognitive and structural brain measures. Neurology, 91(21). doi:10.1212/WNL.0000000000006549
Ouanes, S., & Popp, J. (2019). High Cortisol and the Risk of Dementia and Alzheimer’s Disease - A Review of the Literature. Frontiers in Aging Neuroscience. doi: 10.3389/fnagi.2019.00043
Puetz, V. B., Parker, D., et al. (2017). Altered brain network integrity after childhood maltreatment: A structural connectomic DTI-study. Human Brain Mapping, 38(2), 855-868. doi:10.1002/hbm.23423
Worth, M., Huijbers, W., & Lange, C. (2019). Cortisol associated with hypometabolism across the Alzheimer’s disease spectrum. bioRxiv. doi: 10.1101/514968
This page was first posted April 7, 2005.