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The Neurobiology of Stress: The Stress Response Explained

(Editor’s note: below you have part 4 of the 6-part The Neu­ro­bi­ol­o­gy of Stress series. If you are join­ing the series now, you can read the pre­vi­ous part Here.)

Stayin’  Alive

Under­stand­ing the Human Brain and How It Responds to Stress

THE STRESS RESPONSE EXPLAINED

Stress was put on the map, so to speak, by a Hun­gar­i­an — born Cana­di­an endocri­nol­o­gist named Hans Hugo Bruno Selye (ZEL — yeh) in 1950, when he pre­sent­ed his research on rats at the annu­al con­ven­tion of the Amer­i­can Psy­cho­log­i­cal Asso­ci­a­tion. To explain the impact of stress, Selye pro­posed some­thing he called the Gen­er­al Adap­ta­tion Syn­drome (GAS), which he said had three com­po­nents. Accord­ing to Selye, when an organ­ism expe­ri­ences some nov­el or threat­en­ing stim­u­lus it responds with an alarm reac­tion. This is fol­lowed by what Selye referred to as the recov­ery or resis­tance stage, a peri­od of time dur­ing which the brain repairs itself and stores the ener­gy it will need to deal with the next stress­ful event.

What is crit­i­cal to the impact of stress on kids with LD or ADHD is the third stage of the GAS pro­posed by Selye. He said that if the stress — caus­ing events con­tin­ue, neu­ro­log­i­cal exhaus­tion sets in. This phe­nom­e­non came to be referred to pop­u­lar­ly as burnout. It’s a state of mind char­ac­ter­ized by a loss of moti­va­tion or dri­ve and a feel­ing that you are no longer effec­tive in your work. When this men­tal exhaus­tion sets in, a per­son feels emo­tion­al­ly flat, becomes cyn­i­cal, and may dis­play a lack of respon­sive­ness to the needs of oth­ers. Does this sound like any kids with LD or ADHD that you know?

What’s going on behind the scenes to cause this exhaus­tion? When humans are con­front­ed by phys­i­cal or men­tal stress or injury, an incred­i­bly com­plex and crit­i­cal­ly impor­tant phe­nom­e­non rapid­ly takes place. First to be put on alert is the hypo­thal­a­mus, which is sit­u­at­ed deep inside the brain, under the thal­a­mus and just above the brain stem. It’s only about the size of an almond, but plays a cru­cial role in link­ing the ner­vous sys­tem to the endocrine sys­tem. The hypo­thal­a­mus is par­tic­u­lar­ly inter­est­ing because it con­trols the pro­duc­tion of hor­mones that affect how the body deals with stress. When dan­ger looms, the hypo­thal­a­mus sends a near­ly instan­ta­neous chem­i­cal mes­sage down the spinal cord to the adren­al glands, which are locat­ed just above the kid­neys. This first mes­sage sig­nals the pro­duc­tion of a stress hor­mone called adren­a­line, also called epi­neph­rine, which is released into the blood stream. Nor­ep­i­neph­rine also plays a role here. The inter­ac­tion of these two hor­mones con­trols the amount of glu­cose (sug­ar) in the blood, speeds up the heart rate, and increas­es metab­o­lism and blood pres­sure, all of which get the body ready to respond to the stres­sor.

Mean­while, the hypo­thal­a­mus has been close­ly mon­i­tor­ing these changes, as well as the source of the stress, and now releas­es some­thing called a cor­ti­cotrophin — releas­ing hor­mone (CRH). CRH trav­els along the neu­rons that go from the hypo­thal­a­mus into the pitu­itary gland. This impor­tant gland, which is locat­ed at the base of the brain just above the roof of the mouth, releas­es some­thing called adreno­cor­ti­cotrop­ic hor­mone (ACTH) into the blood­stream. ACTH trav­els down to the adren­al glands. This trig­gers the adren­al glands to release anoth­er hor­mone called cor­ti­sol. (Seri­ous­ly, folks, isn’t this just amaz­ing? )

Some cor­ti­sol (it’s a steroid, by the way — you’ve prob­a­bly used cor­tis one cream to quell some itch) is present in the blood­stream all the time. Nor­mal­ly, it’s present at high­er lev­els in the morn­ing and much low­er at night. Inci­den­tal­ly, recent research has found that the oppo­site is true in some chil­dren with autism, a find­ing that might shed light on this con­di­tion. A lit­tle cor­ti­sol is a good thing. It can give you that quick burst of ener­gy that comes in handy for sur­vival pur­pos­es. For a brief peri­od, it can enhance your mem­o­ry and help boost your immune sys­tem. The right amount of cor­ti­sol helps keep your body sys­tems in a healthy bal­ance, and it can fight against inflam­ma­tion and even low­er your sen­si­tiv­i­ty to pain — all good things when you’ve been injured or if you’re going into bat­tle against a sin­gle stress­ful oppo­nent. But as often hap­pens, too much of a good thing is, well … you know.

The stress response described here tem­porar­i­ly turns down or mod­i­fies nonessen­tial bod­i­ly func­tions and acti­vates the ones we need to keep us safe and healthy. It’s a won­der­ful­ly effi­cient sys­tem, and it’s fine — tuned to do its job well. Our brains and bod­ies are exquis­ite­ly designed to han­dle occa­sion­al acute stress­es or injuries. How­ev­er, they’re not well — equipped to han­dle ongo­ing or chron­ic stress.

Hans Selye’s research on the impact of stress in rats formed the foun­da­tion on which most sub­se­quent stud­ies about stress were built. Over time, and with the aid of sophis­ti­cat­ed brain imag­in­ing tech­nol­o­gy, Selye’s hypoth­e­sis has been scru­ti­nized and expand­ed. He believed that all types of stress result­ed in the same reac­tion in the brain, but we now know that this process is much more com­plex. For exam­ple, con­tem­po­rary research shows that the brain responds in dif­fer­ent ways based on its per­cep­tions of the degree of con­trol that a per­son has over a stress­ful event. Here’s how this plays out in the brain.

The more stress peo­ple are under, or think they are under, the greater the amount of cor­ti­sol that’s pumped into the blood by the adren­al glands. If too much cor­ti­sol is pro­duced (as in acute stress) or is main­tained at high lev­els in the blood­stream for too long (as in chron­ic stress), it can be very harm­ful. This hor­mone can cause a vari­ety of phys­i­cal prob­lems, includ­ing blood sug­ar imbal­ances like hypo­glycemia (a dis­tur­bance in the func­tion­ing of the thy­roid), a decrease in mus­cle tis­sue and bone den­si­ty, and high blood pres­sure. It can also make the body sus­cep­ti­ble to dis­ease by low­er­ing immu­ni­ty and inflam­ma­to­ry respons­es in the body and mak­ing it hard­er for wounds to heal. Pro­longed expo­sure to exces­sive amounts of cor­ti­sol has been impli­cat­ed in the rise of obe­si­ty because too much cor­ti­sol has been shown to be relat­ed to an increase in the amount of abdom­i­nal fat.
Being over­weight can lead to a host of oth­er prob­lems, includ­ing a decrease in “good” cho­les­terol (HDL) and an ele­va­tion of “bad” cho­les­terol (LDL) as well as meta­bol­ic dis­or­ders, heart attacks, and strokes. Most impor­tant to our dis­cus­sion of stress in the lives of stu­dents with LD and ADHD is that too much cor­ti­sol can cause brain changes that result in impaired cog­ni­tive per­for­mance.

To Be Con­tin­ued…

  • Novem­ber 14th: The Human Brain Likes Bal­ance
  • Novem­ber 21st: To Fight, Flee or Freeze –That is the Ques­tion

Jerome J. Schultz, Ph.D., the Author of Nowhere to Hide: Why Kids with ADHD and LD Hate School and What We Can Do About It (Jossey-Bass; August 2011), is a clin­i­cal neu­ropsy­chol­o­gist and is on the fac­ulty of Har­vard Med­ical School in the Depart­ment of Psy­chi­a­try. He served until recent­ly as the Co-Direc­tor of the Cen­ter for Child and Ado­les­cent Devel­op­ment, CCAD, a mul­ti-dis­ci­pli­nary diag­nos­tic and treat­ment clin­ic which is a ser­vice of the Cam­bridge Health Alliance, a Har­vard Teach­ing Hos­pi­tal.

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