After about age 50, most peo­ple begin to expe­ri­ence a decline in mem­ory capa­bil­ity. Why is that? One obvi­ous answer is that the small arter­ies of the brain begin to clog up, often as a result of a life­time of eat­ing the wrong things and a lack of exer­cise. If that life­time has been stress­ful, many neu­rons may have been killed by stress hor­mones. Given the most recent sci­en­tific lit­er­a­ture, reviewed in my book Thank You, Brain, For All You Remem­ber. What You For­got Was My Fault, dead neu­rons can’t be replaced, except in the hip­pocam­pus, which is for­tu­nate for mem­ory because the hip­pocam­pus is essen­tial for mak­ing cer­tain kinds of mem­o­ries per­ma­nent. Another cause is incip­i­ent Alzheimer’s dis­ease; autop­sies show that many peo­ple have the lesions of the dis­ease but have never shown symp­toms, pre­sum­ably because a life­time of excep­tional men­tal activ­ity has built up a “cog­ni­tive reserve.

So is there any­thing you can do about it besides exer­cise like crazy, eat healthy foods that you don’t like all that much, pop your statin pills, and take up yoga?

Yes. In short: focus, focus, focus.

Chang­ing think­ing styles can help. Research shows that older peo­ple tend to have lost some of their abil­ity to pay atten­tion, which for­tu­nately can be improved if they work at it. More specif­i­cally, older peo­ple tend to have dif­fi­culty in ignor­ing dis­trac­tions and irrel­e­vant stim­uli. Dis­trac­tions and a reduced abil­ity to focus dis­rupt the con­sol­i­da­tion process that con­verts work­ing mem­ory into long-lasting form.

In one study of this aging prob­lem, a typ­i­cal group of tri­als involved pre­sent­ing a pic­ture of a face for about a sec­ond, a pic­ture of a scene for about a sec­ond, then a pic­ture of another face for about a sec­ond, and then another pic­ture of a dif­fer­ent scene for about a sec­ond.  Then after a nine-second delay a pic­ture was pre­sented and the sub­ject was instructed to press a but­ton to indi­cate whether the stim­u­lus matched one of the pre­vi­ously pre­sented stim­uli. In other words, the sub­ject had to sup­press the mem­ory of irrel­e­vant stim­uli. In this study (Gaz­za­ley,  et al.  2005) the inves­ti­ga­tors went beyond behav­ioral assess­ment of the responses, because that kind of thing had been done before.  What they wanted to know was what was hap­pen­ing in the brain dur­ing this sup­pres­sion of irrel­e­vant task. They used func­tional mag­netic res­o­nance (fMRI) imag­ing over a region of brain that was respon­sive to the visual images.  What was being mea­sured was the amount of brain activ­ity under con­di­tions when the instruc­tions were to remem­ber a type of image or ignore it.  What they found was that brain activ­ity in all of the young sub­jects increased when they were view­ing scenes they were asked to remem­ber and decreased when pre­sented with an image that they were sup­posed to have ignored. That is, the brain sup­pressed its response to irrel­e­vant stim­uli.  Many older par­tic­i­pants, how­ever, were unable to sup­press brain activ­ity when pre­sented with stim­uli that they had been asked to ignore.  So what these data sug­gest is that older indi­vid­u­als have dif­fi­culty in ignor­ing irrel­e­vant or dis­tract­ing infor­ma­tion that is con­tained in work­ing mem­ory.  But let us not come away with the con­clu­sion that mem­ory deficits in the elderly are inevitable, when in fact in this study nearly half of the elderly showed no deficit.

In a study at the Uni­ver­sity of Illi­nois (Fabi­ani, M. et al. 2006.), researchers recorded brain elec­tri­cal responses in young adults and old sub­jects (65–78) who were pas­sively lis­ten­ing to bursts of sound that con­tained a base fre­quency of 500 cycles per sec­ond, with super­im­posed higher fre­quen­cies at lower ampli­tude. Sound vol­ume was adjusted to the hear­ing thresh­old for each sub­ject. Sound was pre­sented while sub­jects were instructed to con­cen­trate on read­ing a book and to ignore the sound bursts. Four bursts were deliv­ered with vari­able silent inter­vals. The brain reg­is­tered the mem­ory of each burst in the size of the evoked elec­tri­cal response. The rep­e­ti­tion of sound burst was expected to induce sup­pres­sion of the sound-evoked elec­tri­cal response to later bursts in the train, while the silent inter­val was expected to allow for recov­ery as the mem­ory of a pre­ced­ing burst decays. By vary­ing the inter­val, researchers could eval­u­ate the decay process.

Results revealed that the elec­tri­cal responses per­sisted longer in older peo­ple, but the effects of delay inter­val were the same irre­spec­tive of age. Since age did not seem to affect mem­ory decay, one is left to con­clude that the brains of older sub­jects were less able to inhibit the sound burst dis­trac­tions. The good news for the elderly is that age does not make you for­get any faster. It does, appar­ently, make you more distractible.

Such stud­ies should prob­a­bly also be done in chil­dren, who I would sus­pect are more like older peo­ple in being less able to inhibit distractions.

A study at the Uni­ver­sity of Toronto (Grady, C. L. et al. 2006.) used MRI imag­ing of peo­ple while they per­formed a vari­ety of mem­ory tasks, both dur­ing encod­ing and recog­ni­tion. They found an age-related increase in activ­ity in brain areas that nor­mally decrease dur­ing task per­for­mance. This is inter­preted to indi­cate that these areas nor­mally do not respond dur­ing a mem­ory task because the brain is pay­ing atten­tion to the task and assign­ing the mem­ory work only to the parts of brain that need to process the mem­ory. How­ever, another inter­pre­ta­tion is that as you get older, your brain has to recruit more help from other parts of the brain. A related find­ing of the research was an age-related decrease of activ­ity in brain areas that nor­mally become acti­vated dur­ing the mem­ory task. The researchers thought that this find­ing indi­cated an age-related decline in abil­ity to dis­tin­guish task-related demands from those that were irrel­e­vant. It could also be that as you age, the cir­cuits that are nor­mally needed to han­dle mem­ory are less capa­ble. How­ever you look at it, the find­ings doc­u­ment an age-related decline in the brain’s abil­ity to focus its neural resources on mem­ory tasks. What may be most trou­ble­some to con­tem­plate is that the brain activity-pattern changes showed signs of decline around age 40.

So, what do we do about atten­tion deficit? One pos­si­bil­ity is that by keep­ing our brain work­ing hard as we age, we might reduce this ten­dency to lose abil­ity to han­dle mem­ory work­load. Think of it like exer­cise for the brain, which strength­ens the neural cir­cuits in the parts of the brain that have to dis­tin­guish irrel­e­vant from rel­e­vant infor­ma­tion in mem­ory tasks and those parts of the brain that have to do the mem­ory work. Another gen­eral strat­egy is to reduce the dis­trac­tions in our life, at least dis­trac­tions that are present when we are try­ing to remem­ber some­thing. Multi-tasking is hard enough to do when you are young. That abil­ity prob­a­bly declines markedly as you get older. On those occa­sions when I for­get what I opened the refrig­er­a­tor door for, it is always because I let myself get dis­tracted between the time I decided what I wanted and the time when I opened the door. Obvi­ously, older peo­ple (and chil­dren) need to work at pay­ing atten­tion, dis­ci­plin­ing the brain to con­cen­trate. Sec­ond, since they are so dis­tractible, infor­ma­tion should be absorbed in smaller, more man­age­able chunks. By low­er­ing the mem­ory demand, the brain’s lim­ited resources can deal with it more effectively.

— W. R. (Bill) Klemm, D.V.M., Ph.D. Sci­en­tist, pro­fes­sor, author, speaker As a pro­fes­sor of Neu­ro­science at Texas A&M Uni­ver­sity, Bill has taught about the brain and behav­ior at all lev­els, from fresh­men, to seniors, to grad­u­ate stu­dents to post-docs. His recent books include Thank You, Brain, For All You Remem­ber. What You For­got Was My Fault and Core Ideas in Neu­ro­science.

Sources:

- Fabi­ani, M. et al. 2006. Reduced sup­pres­sion or labile mem­ory? Mech­a­nisms of inef­fi­cient fil­ter­ing of irrel­e­vant infor­ma­tion in older adults. J. Cog­ni­tive Neu­ro­science. 18 (4): 637–650.

- Gaz­za­ley, A.  et al.  2005. Top-down sup­pres­sion deficit under­lies work­ing mem­ory impair­ment in nor­mal aging.  Nature Neu­ro­science. 8: 1298–1300.

- Grady, C. L. et al. 2006. Age-related changes in brain activ­ity across the adult lifes­pan. J. Cog­ni­tive Neu­ro­science. 18:227–241.