Sharp Brains: Brain Fitness and Cognitive Health News

Neuroplasticity, Brain Fitness and Cognitive Health News

Icon

The Neurobiology of Stress: Gray Matters

(Editor’s note:  below you have part 2 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

Gray Mat­ters

The term gray mat­ter usu­al­ly evokes an image of the cor­tex, because that ’ s the part most vis­i­ble in pic­tures of the brain.  In fact, gray mat­ter makes up not only the cere­bral cor­tex but also the cen­tral por­tion of the spinal cord and areas called the cere­bel­lar cor­tex and the hip­pocam­pal cor­tex.  This dense tis­sue is packed full of neu­ronal cells, their den­drites (branch­ing, root — like end­ings), axon ter­mi­nals (the oth­er end), and those sticky glial cells I men­tioned ear­li­er. The cor­tex is the area of the brain where the actu­al pro­cess­ing of infor­ma­tion takes place.  Because of its rel­a­tive size and com­plex­i­ty, it ’ s easy to under­stand why it plays a key role in mem­o­ry, atten­tion, per­cep­tu­al aware­ness, thought, lan­guage, and con­scious­ness.

A Divi­sion of Labor

A cen­tral groove, or fis­sure, runs from the front to back of the cor­tex, divid­ing it into right and left hemi­spheres. In gen­er­al, the left hemi­sphere con­trols func­tions on the right side of the human body and the right hemi­sphere con­trols the left side, but there are sig­nif­i­cant excep­tions and much sophis­ti­cat­ed inter­ac­tion between the two hemi­spheres. This com­mu­ni­ca­tion between the left and right hemi­spheres is facil­i­tat­ed by the cor­pus cal­lo­sum, a wide, fl at bun­dle of axons locat­ed in the cen­ter of the brain, beneath the cor­tex. Think of it as the Lin­coln Tun­nel, con­nect­ing Man­hat­tan and Jer­sey City. (I ’ ll leave it to you to decide which one rep­re­sents which hemi­sphere.)

The cor­pus cal­lo­sum makes up the largest area of so — called white mat­ter in the brain. White mat­ter is made of bun­dles of axons each encased in a sheath of myelin. These nerve bun­dles lead into and out of the cor­tex and the cere­bel­lum, and branch to the “ old brain, ” the hip­pocam­pus. About 40 per­cent of the human brain is made up of gray mat­ter, and the oth­er 60 per­cent is white mat­ter. It’s the white mat­ter that facil­i­tates com­mu­ni­ca­tion between dif­fer­ent gray mat­ter areas and between the gray mat­ter and the rest of the body. White mat­ter is the Inter­net of our brains. (Al Gore did not invent it.)

Evo­lu­tion, tem­pered by expe­ri­ence, has employed gray mat­ter to build what might be con­sid­ered very well — devel­oped “ cog­ni­tive con­dos ” that sit above the hip­pocam­pus. This arrange­ment is very impor­tant to a dis­cus­sion of stress. Our old or prim­i­tive brain was primed for sur­vival in our ances­tors ’ envi­ron­ment. It’s inter­est­ing to note that the brains of low­er ver­te­brates like fish and amphib­ians have their white mat­ter on the out­side of their brain. We are blessed (and cursed) with lots of gray mat­ter that gives us the abil­i­ty to think things through (espe­cial­ly if we are anx­ious). Frogs and sala­man­ders and their pond — side friends don’t think about dan­ger so much — they just get out of its way! (And while I can ’ t be sure, I don ’ t think that they have night­mares about giant human chil­dren armed with nets.)

How do you feel about that? In case you ever get this ques­tion on Jeop­ardy or in a game of Triv­ial Pur­suit, the lim­bic sys­tem is made up of the amyg­dala, the hip­pocam­pus, the cin­gu­late gyrus, for­ni­cate gyrus, hypo­thal­a­mus, mam­mil­lary body, epi­thal­a­mus, nucle­us accum­bens, orbitofrontal cor­tex, parahip­pocam­pal gyrus, and thal­a­mus. These struc­tures work togeth­er to process emo­tions, moti­va­tion, the reg­u­la­tion of mem­o­ries, the inter­face between emo­tion­al states and mem­o­ry of events, the reg­u­la­tion of breath­ing and heart rate, the pro­duc­tion of hor­mones, the “ fight or flight ” response, sex­u­al arousal, cir­ca­di­an rhythms, and some deci­sion — mak­ing sys­tems. Pret­ty impres­sive job descrip­tion, eh? The word lim­bic comes from the Latin word lim­bus, which trans­lates to “ belt ” or “ bor­der, ” because this sys­tem forms the inner bor­der of the cor­tex. The lim­bic sys­tem is part of the old brain and devel­oped first, fol­lowed by the new brain: the cor­tex, which is some­times referred to as the neo­cor­tex. Put very sim­ply, the lim­bic sys­tem feels and remem­bers; the cor­tex acts and reacts. And they com­mu­ni­cate with each oth­er. Why is this impor­tant? The lim­bic sys­tem fig­ures promi­nent­ly in what ’ s called the stress response, which is a cen­tral play­er in this book.

These days, both our old and new brains are acti­vat­ed when we ’ re under stress. The prim­i­tive part, the lim­bic sys­tem (notably the hip­pocam­pus), sniffs out dan­ger well before the new brain (the neo­cor­tex) actu­al­ly process­es it. The old brain responds first, act­ing as a sort of fi re alarm sys­tem. It is the neo­cor­tex, and in par­tic­u­lar, the frontal lobe (the pre-frontal cor­tex), that helps us make sense of the alarms.

The cor­tex is made up of four major sec­tions, arranged from the front to the back. These are called the frontal, pari­etal, occip­i­tal, and tem­po­ral lobes. Each of the four lobes is found in both hemi­spheres, and each is respon­si­ble for dif­fer­ent, spe­cial­ized cog­ni­tive func­tions. For exam­ple, the occip­i­tal lobe con­tains the pri­ma­ry visu­al cor­tex, and the tem­po­ral lobe (locat­ed by the tem­ples, and close to the ears) con­tains the pri­ma­ry audi­to­ry cor­tex.

The frontal lobes are posi­tioned at the front most region of the cere­bral cor­tex and are involved in move­ment, deci­sion mak­ing, prob­lem solv­ing, and plan­ning. There are three main divi­sions of the frontal lobes. They are the pre­frontal cor­tex, the pre­mo­tor area, and the motor area. The frontal lobe of the human brain con­tains areas devot­ed to abil­i­ties that are enhanced in or unique to humans. The pre­frontal cor­tex is respon­si­ble for plan­ning com­plex cog­ni­tive behav­iors, the expres­sion of per­son­al­i­ty, deci­sion mak­ing, and social behav­ior, as well as the orches­tra­tion of thoughts and actions nec­es­sary for a per­son to car­ry out goals. A spe­cial­ized area known as the ven­tro­lat­er­al pre-frontal cor­tex has pri­ma­ry respon­si­bil­i­ty for the pro­cess­ing of com­plex lan­guage. It is more com­mon­ly called Bro­ca ’ s area, named for a nine­teenth — cen­tu­ry French physi­cian who deter­mined its role.

In humans and oth­er pri­mates, an area locat­ed at the for­ward part of the pre­frontal cor­tex is called the orbitofrontal cor­tex. It gets its name from its posi­tion imme­di­ate­ly above the orbits, the sock­ets in which the eyes are locat­ed. The orbitofrontal cor­tex is very involved in inter­pret­ing rewards, deci­sion mak­ing, and pro­cess­ing social and emo­tion­al infor­ma­tion. For this rea­son, some con­sid­er it to be a part of the lim­bic sys­tem.

The amyg­dala, a part of the lim­bic sys­tem, is a brain struc­ture that is respon­si­ble for decod­ing emo­tions, espe­cial­ly those the brain per­ceives as threats. As we evolved as a species, many of our alarm cir­cuits have been grouped togeth­er in the amyg­dala. Not sur­pris­ing­ly, many regions of the brain send neu­rons into the amyg­dala. As a result, lots of sen­so­ry mes­sages trav­el instan­ta­neous­ly to the amyg­dala to inform it of poten­tial dan­gers lurk­ing in our neigh­bor­hood. The amyg­dala is our guard dog.

The amyg­dala is direct­ly wired to the hip­pocam­pus, also a part of the lim­bic sys­tem. Since the hip­pocam­pus is involved in stor­ing and retriev­ing explic­it mem­o­ries, it feeds the amyg­dala with strong emo­tions trig­gered by these rec­ol­lec­tions. Why is this impor­tant? If a child has a neg­a­tive expe­ri­ence in school, like being ter­ri­bly embar­rassed when asked to read in front of the class, the hip­pocam­pus just won’ t let go of this mem­o­ry, and it shouts it out to the amyg­dala. Since the amyg­dala has signed a no con­fi­den­tial­i­ty agree­ment, it sends a warn­ing to the rest of the brain to go into pro­tec­tion mode. A rather amaz­ing arrange­ment, don’t you think?

What’s real­ly inter­est­ing about this is that the hip­pocam­pus spe­cial­izes in pro­cess­ing the con­text of a sit­u­a­tion. As a result, the child under stress gen­er­al­izes the entire sit­u­a­tion and uses it as jus­ti­fi cation for anx­i­ety or stress: “ Hey, they’re telling me to go to social stud­ies class. ”Even though not every­thing about social stud­ies may be a threat — per­haps just the fact that they read out loud in there — the hip­pocam­pus sends out a gen­er­al alert. So the stu­dent responds by protest­ing the whole enchi­la­da: “No way I’m going there.”

The amyg­dala is also wired to the medi­al pre­frontal cor­tex. Want to know why this is impor­tant? This is the area of the brain that seems to be involved in plan­ning a spe­cif­ic response to a threat to safe­ty. Here ’ s how it works: the child is hit with the gigan­tic Titan­ic news (which may be just “social stud­ies com­ing up next” to the rest of the group, but it’s “Sub­merged ice­berg ahead!” to the kid wor­ried about per­ceived hor­rors there). This two — way  com­mu­ni­ca­tion between the pre­frontal cor­tex and the lim­bic sys­tem (par­tic­u­lar­ly the amyg­dala) enables us to exer­cise con­scious con­trol over our anx­i­ety. The emo­tion — cog­ni­tion con­nec­tion allows us to feel that we can do some­thing about the dan­ger that lies ahead. The child is then faced with the neces­si­ty of choos­ing a course of action that looks best for get­ting out of dan­ger. This seems very pro­tec­tive but tends to be coun­ter­pro­duc­tive, because the very mech­a­nism that allows us to cre­ate an escape plan can actu­al­ly cre­ate anx­i­ety. “ Oh crud — now we have to do some­thing! ” The brain not only allows us to imag­ine a neg­a­tive out­come, which can help us avoid dan­ger, it makes it pos­si­ble for us to imag­ine dan­gers that do not actu­al­ly exist. This is a prob­lem for chil­dren who have ADHD, and a huge prob­lem for stu­dents who have both anx­i­ety dis­or­ders and ADHD. If you do a brain scan of a per­son with ADHD while putting on pres­sure to per­form in a cer­tain way, you see that this “to do” order results in a decrease in activ­i­ty in the pre­frontal cor­tex (instead of increas­ing it, as it does in most peo­ple). This helps explain why kids with ADHD don ’ t respond well to lists. These are read as “thou shalt” mes­sages. What helps some of us stay orga­nized sends some kids with ADHD up the wall.

The Thal­a­mus Bone’s Con­nect­ed to the …

Of course, it’s not real­ly a bone; it’s a plum — shaped mass of gray
mat­ter that’s mul­ti­lay­ered and mul­ti­fac­eted. The thal­a­mus, anoth­er part of the lim­bic sys­tem, sits on top of the hypo­thal­a­mus which, in turn, sits on top of the brain stem, which is in the cen­ter of the base of the brain. This is a great loca­tion for the thal­a­mus because it acts as a relay sys­tem that sends nerve fi bers upstairs to all parts of the cere­bral cor­tex as well as many sub-cor­ti­cal (under­neath the cor­tex) parts of the brain. The thal­a­mus receives infor­ma­tion from every sen­so­ry organ and its asso­ci­at­ed neu­rons except the olfac­to­ry (smell) sys­tem. The hypo­thal­a­mus gets infor­ma­tion from the eyes, the ears, the skin, and the tongue, and it for­wards these mes­sages to the cor­re­spond­ing areas of the cor­tex where they are processed. In terms of stress, this relay sys­tem is how the brain knows that it’s in a dan­ger­ous envi­ron­ment.

That Stinks!

There’s a bulb — shaped brain struc­ture (called, as you might guess, the olfac­to­ry bulb ) that has the spe­cial­ized task of mak­ing sense of scents. Think about this: you can’t see when you are sleep­ing, but you can smell. This is awful­ly help­ful at night, espe­cial­ly when there’s a fire. And when you get hold of a bad piece of fish. That’s prob­a­bly why the nose gets its own spe­cial recep­tor. It’s anoth­er exam­ple of how sen­si­tive the brain is to changes in the envi­ron­ment, and how it’s always on alert!

To Be Con­tin­ued…

  • Octo­ber 31st: The Lit­tle Brain Down Under
  • Novem­ber 7th:Stress Response Explained
  • Novem­ber 14th: The Human Brain Likes Bal­ance
  • Novem­ber 21st: To Fight, Flee or Freeze –That is the Ques­tion

Jerome Schultz 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.

Relat­ed arti­cles:

Leave a Reply...

Loading Facebook Comments ...

Leave a Reply

Categories: Attention and ADD/ADHD, Author Speaks Series, Education & Lifelong Learning, Health & Wellness

Tags: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,

About SharpBrains

As seen in The New York Times, The Wall Street Journal, BBC News, CNN, Reuters,  SharpBrains is an independent market research firm tracking how brain science can improve our health and our lives.

Search in our archives

Follow us and Engage via…

twitter_logo_header
RSS Feed

Watch All Recordings Now (40+ Speakers, 12+ Hours)