Feb 5, 2008
By: Alvaro Fernandez
Below you have a very insightful article on stress by one of our new Expert Contributors, Gregory Kellet, a researcher at UCSF. Enjoy! (Credit for Pic of Victoria Crater in Mars: Mars Reconnaissance Orbiter, via Wikipedia).
“My brain is fried, toast, frazzled, burnt out. How many times have you said or heard one version or another of these statements. Most of us think we are being figurative when we utter such phrases, but research shows that the biological consequences of sustained high levels of stress may have us being more accurate than we would like to think.
Crash Course on Stress
Our bodies are a complex balancing act between systems working full time to keep us alive and well. This balancing act is constantly adapting to the myriad of changes occurring every second within ourselves and our environments. When it gets dark our pupils dilate, when we get hot we sweat, when we smell food we salivate, and so forth. This constant balancing act maintains a range of stability in the body via change; and is often referred to as allostasis. Any change which threatens this balance can be referred to as allostatic load or stress.
Allostatic load/stress is part of being alive. For example just by getting up in the morning, we all experience a very important need to increase our heart rate and blood pressure in order to feed our newly elevated brain. Although usually manageable, this is a change which the body needs to adapt to and, by our definition, a stressor.
Stress is only a problem when this allostatic load becomes overload. When change is excessive or our ability to adapt is compromised, things start to go wrong. We will focus here on what seems to be happening in the brain under such conditions.
Whether it’s getting up in the morning, worrying about the non-existent past/future, or getting angry at your last parking ticket, stress takes energy. One of the major roles of the infamous fight or flight response is to mobilize energy, and it does this well. If you need to run away from a swarm of killer bees or fend off an attacking bear, you will be assisted by various chemicals produced within the body. These include the well-known adrenaline–now more commonly referred to as epinephrine–and a lesser known group of chemicals known as the glucocorticoids, most notably cortisol. Both epinephrine and the glucocorticoids are involved in making stored energy available for use in the form of fats and sugars. Epinephrine does so over the short term (within seconds) while glucocorticoids act over a longer period (minutes to hours). Let’s look at the effects of the later of the two, the glucocorticoids.
Your Brain on Stress
Cortisol, the most prominent of the glucocorticoids, does an excellent job of allowing us to adapt to most stressors which last more than a couple of minutes but under an hour. Short term it will actually enhance our immune system, memory and attention. Long term, past ½ hour to an hour, excessively elevated cortisol levels start to have detrimental effects. It seems we were designed more to deal with short spurts of high stress, such as beating back that attacking bear, rather than long drawn-out stressors such as meeting deadlines.
Our brains appear to be most vulnerable to the effects of excessive stress in a region called the hippocampus. The hippocampus is a mass of neurons each with multiple branch-like extensions (dendrites and axons) which make connections (synapses) with other neurons all across the brain. Among other things, this region is important in dealing with emotions and consolidating new memories. As with all brain regions, its ability to adapt relies upon being able to alter the branching and connections of its neurons. The hippocampus is also one of the only regions of the brain known to be able to produce new neurons, a process called neurogenesis.
Enduring a high stressor for more than 30 minutes to an hour has been shown to negatively impact the hippocampus in various ways. To begin, sustained exposure to higher than normal levels of cortisol results in the pruning back of the number of branches and synaptic connections of hippocampal neurons. By a variety of mechanisms, these conditions also increase the rate of cell death in this region of the brain.
As if this wasn’t bad enough, recent research is also demonstrating that sustained increases in glucocorticoid levels also has negative effects, impairing the hippocampus’s ability to create new neurons.
Over a period of time, all of this results in the shrinking in size of the hippocampus with associated declines in cognitive function, including the ability to retain new information and adapt to novel situations.
Fortunately the negative effects of excessive stress can not only be stopped but also reversed once the source (psychological or physical) is removed or sufficiently reduced. Next time we will explore techniques one can use to protect our brains by managing the unavoidable stressors we all face as part of being human.
For more indepth information featuring one of the leading expert researchers on the subject of stress, check out the following video (1 hour 20 minutes): Robert Sapolsky.
— Gregory Kellett has a masters in Cognitive Neurology/Research Psychology from SFSU and is a researcher at UCSF where he currently investigates the psychophysiology of social stress. He wrote this article for SharpBrains.com to contribute to our public education initiative.
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