23 de agosto de 2012

Cambios cerebrales en las víctimas de Bullying

The Neurobiology of Stress: The Human Brain Likes to Be in Balance
By: Dr. Jerome Schultz

(Editor’s note: below you have part 5 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 Human Brain Likes to Be in Balance

For­tu­nately, the brain has some built — in safety sys­tems. Too much cor­ti­sol in the blood sig­nals the brain and adrenal glands to decrease cor­ti­sol pro­duc­tion. And under nor­mal con­di­tions, when the stress is over­come or brought under con­trol (by fight­ing, flee­ing, or turn­ing into an immo­bile statue, or by mas­ter­ing the threat), the hypo­thal­a­mus starts send­ing out the orders to stand down. Stop pro­duc­ing cor­ti­sol!  Event over!  Under con­tin­u­ous stress, how­ever, this feed­back sys­tem breaks down. The hypo­thal­a­mus keeps read­ing the stress as a threat, furtively send­ing mes­sages to the pitu­itary gland, which screams out to the adrenal glands to keep pump­ing out cor­ti­sol, which at this point begins to be neu­ro­toxic — poi­son to the brain.
Bruce Perry and Ron­nie Pol­lard, a well — respected psy­chi­a­trist — neu­rol­o­gist team, have con­tributed much to our under­stand­ing of the impact of stress and how it affects this sense of bal­ance, or home­osta­sis, in the brain. Some­times when stress is so intense, the del­i­cate inter­ac­tion among the brain sys­tems designed to han­dle it are thrown off bal­ance. Other researchers have also shown that intense, acute, or trau­matic stress presents such a shock to the brain and the stress response sys­tem that it actu­ally reor­ga­nizes the way the brain responds to stress. For exam­ple, neu­roen­docri­nol­o­gist Bruce McEwen and neu­ro­sci­en­tist Frances Cham­pagne have shown that repeated acti­va­tion of the stress response can result in phys­i­cal changes, caused by too many inflam­ma­tory pro­teins being pumped into the blood­stream. The research of Michael Meany, a neu­ro­bi­ol­o­gist at McGill Uni­ver­sity, shows that adverse early child­hood events (trau­mas) can actu­ally change the chem­istry of DNA in the brain. By a process known as methy­la­tion, lit­tle chem­i­cal mark­ers attach them­selves to the genes that con­trol the stress hor­mone recep­tors. This makes it hard for the brain to reg­u­late its response to stress.

 Let me explain it this way: It’s rather like the keys of a piano being hit so hard that the impact puts the strings out of tune. The piano still plays, but it plays dif­fer­ently. While another hard hit on the keys might have bro­ken a tuned piano wire, the now — slack wire can with­stand another hit … and another. If the hits are even harder, the wire stretches more. You can almost hear the piano (and the brain under acute stress) say­ing, “Go on, hit me again! I can take it.” But the cost is that both are out of tune and the melody is never quite the same.  In the human ner­vous sys­tem, this kind of adjust­ment or adap­ta­tion pro­tects the brain from harm by chang­ing the way it responds to stress. Perry and Pol­lard point out that repeated expo­sure to stress — chronic stress — results in a new way of cop­ing with a con­tin­u­ous stres­sor, but it is less effec­tive.  Not a good thing.
Both repeated trau­mas and chronic stress can result in a num­ber of bio­log­i­cal reac­tions. Neu­ro­chem­i­cal sys­tems are affected that can cause a cas­cade of changes in atten­tion, impulse con­trol, sleep, and fine motor con­trol. Other researchers have zeroed in on spe­cific parts of the brain that are affected by stress, and their work shows us just how refined and com­plex this process is. For exam­ple, Walker, Toufexis, and Davis sug­gest that an area of the brain called the bed nucleus of the stria ter­mi­nalis plays a role in cer­tain types of anx­i­ety and stress responses. Although this area is not thought to be involved in acute trau­matic events, these authors have shown that it is respon­si­ble for pro­cess­ing the slower — onset, longer — last­ing responses that fre­quently accom­pany sus­tained threats. (Aha!)  These authors fur­ther posit that the phys­i­o­log­i­cal reac­tions in this area may per­sist even after the threat goes away. (Ah — HA!! ) Why is this rel­e­vant? Even when teach­ers and other pro­fes­sion­als try to get these kids to move for­ward, the mem­ory of past trau­matic events lingers on — and impedes efforts to lead stu­dents to a higher level of competence.

All of this research has incred­i­ble sig­nif­i­cance in the dis­cus­sion of kids who are under stress as a con­se­quence of their LD and ADHD. It also has impli­ca­tions for stu­dents with other dis­or­ders, such as Asperger syn­drome and autism. Pol­lard and Perry tell us that chronic acti­va­tion of cer­tain parts of the brain involved in the fear response, such as the hypo­thal­a­mic — pitu­itary — adrenal (HPA) axis, can wear out other parts of the brain such as the hip­pocam­pus, which is involved in cog­ni­tion and mem­ory. Again, cog­ni­tion and mem­ory: two of the most impor­tant build­ing blocks for suc­cess­ful learn­ing, atten­tion, and social communication.


What ’ s Bul­ly­ing Got to Do with It?
The under­ly­ing the­sis of this book is that chronic stress changes brain chem­istry and there­fore brain func­tion. This con­nec­tion is made even stronger by a bur­geon­ing amount of provoca­tive new research that sheds light on the adverse impact of bul­ly­ing on the brains of vic­tims. Dr. Mar­tin Teicher, a neu­ro­sci­en­tist at McLean Hos­pi­tal, a Har­vard teach­ing hos­pi­tal, scanned the brains of young adults who reported that they had been bul­lied by peers when they were younger. The brain cells in their cor­pus cal­lo­sum, that fibrous bun­dle of tis­sue that con­nects the two hemi­spheres of the brain, showed evi­dence of cel­lu­lar changes that were not seen in a com­pa­ra­ble group of stu­dents who had not been bul­lied. The neu­rons in this part of the brains of vic­tims had less myelin, that is, less of the pro­tec­tive coat­ing that cov­ers the nerves.  Since myelin facil­i­tates com­mu­ni­ca­tion between cells, reduced myelin results in a slow­down in the trans­mis­sion of brain sig­nals. Rapid and effi­cient trans­mit­tal of neu­ro­log­i­cal impulses in the brain is a pre­req­ui­site for effec­tive learn­ing and memory.

Here ’ s the rea­son this is so impor­tant to the dis­cus­sion of stress: because of the dif­fer­ences that many chil­dren with LD and ADHD exhibit (impul­sive behav­ior, poor recep­tive and expres­sive lan­guage, poor social per­cep­tion, and so on), they are more likely than other chil­dren to be vic­tims of bul­ly­ing. This is borne out both by research and by clin­i­cal observation.

What is clear is that a slow­down in neural trans­mis­sion in the still — devel­op­ing brains of young peo­ple affects learn­ing, mem­ory, and emo­tional reac­tiv­ity.  Dr. Tracy Vail­lan­court, a psy­chol­o­gist at the Uni­ver­sity of Ottawa, and her col­leagues found that both occa­sional and fre­quent bul­ly­ing can recal­i­brate the amount of the stress hor­mone cor­ti­sol pro­duced by a group of twelve — year — old vic­tims. Inter­est­ingly, she also found that boys who had been bul­lied had very high lev­els of cor­ti­sol, while cor­re­spond­ing lev­els were abnor­mally low in girls who had been harassed.  The exact rea­sons are yet unclear, but we do know that the amount of cor­ti­sol is reset or recal­i­brated in peo­ple and ani­mals that are in a state of chronic stress. If girls are neu­ro­bi­o­log­i­cally more vul­ner­a­ble to stress, this might account for the dif­fer­ence. Dr. Vail­lan­court points out that high lev­els of cor­ti­sol can dam­age and even kill neu­rons in the hip­pocam­pus.  The impact of stress dam­age can be seen in the results of for­mal test­ing.  Dr. Vail­lan­court found that bul­lied teens per­formed more poorly than their peers on tests of ver­bal mem­ory.  She con­cludes, “Bul­ly­ing likely dimin­ishes a person’s abil­ity to cope with stress, pos­si­bly plac­ing them at risk for psy­chopathol­ogy and ill health.”

 And here’s another inter­est­ing piece of infor­ma­tion gen­er­ated by Mar­tin Teicher’s work that relates to Dr. Vaillancourt’s.  While Teicher did not deter­mine a cause — and — effect rela­tion­ship, he found that stu­dents who had been ver­bally or phys­i­cally harassed reported more psy­chi­atric symp­toms, includ­ing depres­sion and anx­i­ety, than their bully — free classmates.
While addi­tional research is nec­es­sary, it is impos­si­ble to avoid won­der­ing whether the dis­abil­ity — bul­ly­ing — stress con­nec­tion is a sig­nif­i­cant fac­tor in the lives of many of the chil­dren you and I care for and care about.

Fuente original: http://www.sharpbrains.com/blog/2011/11/14/the-neurobiology-of-stress-the-human-brain-likes-to-be-in-balance/