Update: we now have an in-depth inter­view with Yaakov Stern, lead­ing advo­cate of the cog­ni­tive reserve the­ory, and one of the authors of the paper we review below: click on Build Your Cog­ni­tive Reserve-Yaakov Stern. 

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In honor of the Week of Sci­ence pre­sented at Just Sci­ence from Mon­day, Feb­ru­ary 5, through Sun­day, Feb­ru­ary 11, we will be writ­ing about “just sci­ence” this week. We thought we would take this time to dis­cuss more deeply some of the key sci­en­tific pub­li­ca­tions in brain fitness.

Today, we will high­light the key points in an excel­lent review of cog­ni­tive reserve: Scarmeas, Niko­laos and Stern, Yaakov. Cog­ni­tive reserve and lifestyle. Jour­nal of Clin­i­cal and Exper­i­men­tal Neu­ropsy­chol­ogy. 2003;25:625–33.

What is Cog­ni­tive Reserve?
The con­cept of a cog­ni­tive reserve has been around since 1998 when a post mortem analy­sis of 137 peo­ple with Alzheimer’s Dis­ease showed that the patients exhib­ited fewer clin­i­cal symp­toms than their actual pathol­ogy sug­gested. (Katz­man et al. 1988) They also showed higher brain weights and greater num­ber of neu­rons when com­pared to age-matched con­trols. The inves­ti­ga­tors hypoth­e­sized that the patients had a larger “reserve” of neu­rons and abil­i­ties that off­set the losses caused by Alzheimer’s. Since then the con­cept of cog­ni­tive reserve has been defined as the abil­ity of an indi­vid­ual to tol­er­ate pro­gres­sive brain pathol­ogy with­out demon­strat­ing clin­i­cal cog­ni­tive symp­toms.

Despite many stud­ies that demon­strate an asso­ci­a­tion between higher par­tic­i­pa­tion in more intel­lec­tual, social and phys­i­cal activ­i­ties and more reserve, most of these stud­ies were not done over a long enough time period to rule out whether the stim­u­lat­ing activ­i­ties were pro­mot­ing higher cog­ni­tive per­for­mance or higher per­form­ers were more likely to engage in stim­u­lat­ing activ­i­ties. The lon­gi­tu­di­nal stud­ies show a mutu­ally rein­forc­ing cycle between an ini­tially high intel­lec­tual func­tion­ing per­son, an engaged lifestyle, and more cog­ni­tive reserve, but also a main­te­nance of intel­lec­tual per­for­mance. (Arbuckle et al. 1992, Gold et al. 1995, Hultsch et al 1999, Schaie 1984, Schaie 1996, Schooler and Mulatu 2001)

In one study of 1772 non­de­mented indi­vid­u­als over seven years that con­trolled for fac­tors like eth­nic group, edu­ca­tion, and occu­pa­tion, par­tic­i­pants with high leisure activ­ity had 38% less risk of devel­op­ing demen­tia, and that risk was reduced by approx­i­mately 12% for each addi­tional leisure activ­ity adopted. (Scarmeas, Levy, et al. 2001) Later stud­ies, includ­ing imag­ing stud­ies of cere­bral blood flow, con­tinue to build up data show­ing fre­quent par­tic­i­pa­tion in cog­ni­tively stim­u­lat­ing activ­i­ties reduces risk for Alzheimer’s and slows the rate of cog­ni­tive decline. Inter­est­ingly, phys­i­cal, social, and intel­lec­tual activ­i­ties all help, although intel­lec­tual activ­i­ties were asso­ci­ated with the low­est risk of inci­dent demen­tia. Fur­ther­more, it has been shown that peo­ple with high cog­ni­tive reserve decline more rapidly, sup­port­ing the idea that the pathol­ogy is more advanced by the time it is clin­i­cally appar­ent. (Stern, Tang, et al. 1995)

Causal­ity

The asso­ci­a­tion between engaged lifestyle and demen­tia risk could be either medi­ated or con­founded by abil­i­ties like IQ or edu­ca­tion. If this is the case then it could be that either IQ or edu­ca­tion rep­re­sent the true causal links with demen­tia or that sub­jects with higher IQ or edu­ca­tion tend to adopt lifestyles which them­selves causally reduce the risk of demen­tia (such as exer­cise, diet, etc.). Nev­er­the­less, in stud­ies where edu­ca­tion and occu­pa­tion (Scarmeas et al. 2001) or edu­ca­tion and IQ (Scarmeas et al. 2003) were con­trolled for, the asso­ci­a­tion between leisure activ­i­ties and demen­tia risk was still there.

Other pos­si­bil­i­ties are that high func­tion­ing and engaged lifestyle are results of an innate capac­ity. Or per­haps bor­der­line demen­tia patients are less active as a result of the pathol­ogy. Or per­haps the con­nec­tion has yet to be found.

How Does it Work?
If it is a causal rela­tion­ship, there are four pos­si­ble expla­na­tions of how it might work:

1. Par­tic­i­pa­tion in stim­u­lat­ing activ­i­ties spurs neu­ronal growth and a larger num­ber of neu­rons to com­pen­sate for the pathology
2. High activ­ity peo­ple use the same num­ber of neural net­works more efficiently
3. High activ­ity peo­ple use alter­nate neural net­works more effi­ciently to com­pen­sate for the pathology
4. The fac­tors that affect cog­ni­tive reserve dis­rupt the devel­op­ment of the dis­ease pathol­ogy by decreas­ing neurodegeneration

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Update: we now have an in-depth inter­view with Yaakov Stern, lead­ing advo­cate of the cog­ni­tive reserve the­ory, and one of the authors of the paper we review below: click on Build Your Cog­ni­tive Reserve-Yaakov Stern.  

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Fur­ther Reading

• Arbuckle TY, Gold DP, Andres D, Schwartz­man A, Chaikel­son J. The role of psy­choso­cial con­text, age, and intel­li­gence in mem­ory per­for­mance of older men. Psy­chol Aging. 1992;7:25–36.
• Gold DP, Andres D, Etezadi J, Arbuckle T, Schwartz­man A, Chaikel­son J. Struc­tural equa­tion model of intel­lec­tual change and con­ti­nu­ity and pre­dic­tors of intel­li­gence in older men [pub­lished erra­tum appears in Psy­chol Aging 1998;13(3):434]. Psy­chol Aging. 1995;10:294–303.
• Hultsch D, Hert­zog C, Small BJ, Dixon RA. Use it or lose it: Engaged lifestyle as a buffer of cog­ni­tive decline in aging? Psy­chol Aging. 1999;14:245–63.
• Katz­man R, Terry R, DeTeresa R, et al. Clin­i­cal, patho­log­i­cal, and neu­ro­chem­i­cal changes in demen­tia: A sub­group with pre­served men­tal sta­tus and numer­ous neo­cor­ti­cal plaques. Ann Neu­rol. 1988;23:138–44.
• Roe CM, Xiong C, Miller JP, Mor­ris JC. Edu­ca­tion and Alzheimer dis­ease with­out demen­tia: sup­port for the cog­ni­tive reserve hypoth­e­sis. Neu­rol­ogy. 2007;68:223–8.
• Scarmeas N, Levy G, Tang MX, Manly J, Stern Y. Influ­ence of leisure activ­ity on the inci­dence of Alzheimer’s dis­ease. Neu­rol­ogy. 2001;57:2236–42.
• Scarmeas N, Stern Y. Cog­ni­tive reserve and lifestyle. J Clin Exp Neu­ropsy­chol. 2003;25:625–33.
• Scarmeas N, Zarahn E, Ander­son KE, et al. Cog­ni­tive reserve-mediated mod­u­la­tion of positron emis­sion tomo­graphic acti­va­tions dur­ing mem­ory tasks in Alzheimer dis­ease. Arch Neu­rol. 2004;61:73–8.
• Scarmeas N, Zarahn E, Ander­son KE, et al. Asso­ci­a­tion of life activ­i­ties with cere­bral blood flow in Alzheimer dis­ease: impli­ca­tions for the cog­ni­tive reserve hypoth­e­sis. Arch Neu­rol. 2003;60:359–65.
• Schaie KW. Intel­lec­tual devel­op­ment in adult­hood: The Seat­tle lon­gi­tu­di­nal study. San Diego: Aca­d­e­mic Press, 1996.
• Schaie K. Midlife influ­ences upon intel­lec­tual func­tion­ing in old age. Inter­na­tional Jour­nal of Behav­ioral Devel­op­ment. 1984;7:463–78.
• Schooler C, Mulatu MS. The rec­i­p­ro­cal effects of leisure time activ­i­ties and intel­lec­tual func­tion­ing in older peo­ple: A lon­gi­tu­di­nal analy­sis. Psy­chol Aging. 2001;16:466–82.
• Stern Y. Cog­ni­tive reserve and Alzheimer dis­ease. Alzheimer Dis Assoc Dis­ord. 2006;20:S69-74.
• Stern Y. Cog­ni­tive reserve and Alzheimer dis­ease. Alzheimer Dis Assoc Dis­ord. 2006;20:112–7.
• Stern Y, Habeck C, Moeller J, et al. Brain net­works asso­ci­ated with cog­ni­tive reserve in healthy young and old adults. Cereb Cor­tex. 2005;15:394–402.
• Stern Y, Tang MX, Denaro J, Mayeux R. Increased risk of mor­tal­ity in Alzheimer’s dis­ease patients with more advanced edu­ca­tional and occu­pa­tional attain­ment. Ann Neu­rol. 1995;37:590–5.

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