Stress and Neural Wreckage: Part of the Brain Plasticity Puzzle

Feb 5, 2008
By: Alvaro Fernandez

“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.

Energy Mobi­liza­tion

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.

Brain Dam­age

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.

Dam­age Control

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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