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 .Ã‚Â

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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:

Par­tic­i­pa­tion in stim­u­lat­ing activ­i­ties spurs neu­ronal growth and a larg­er num­ber of neu­rons to com­pen­sate for the pathol­o­gy High activ­i­ty peo­ple use the same num­ber of neur­al net­works more effi­cient­ly High activ­i­ty peo­ple use alter­nate neur­al net­works more effi­cient­ly to com­pen­sate for the pathol­o­gy 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 .Ã‚Â Ã‚Â

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Fur­ther Read­ing