Home Featured Post Large neuroimaging study finds social isolation to be an early indicator of increased dementia risk

Large neuroimaging study finds social isolation to be an early indicator of increased dementia risk

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Why do we get a buzz from being in large groups at fes­ti­vals, jubilees and oth­er pub­lic events? Accord­ing to the social brain hypoth­e­sis, it’s because the human brain specif­i­cal­ly evolved to sup­port social inter­ac­tions. Stud­ies have shown that belong­ing to a group can lead to improved well­be­ing and increased sat­is­fac­tion with life.

Unfor­tu­nate­ly though, many peo­ple are lone­ly or social­ly isolated.

And if the human brain real­ly did evolve for social inter­ac­tion, we should expect this to affect it sig­nif­i­cant­ly. Our recent study, pub­lished in Neu­rol­o­gy, shows that social iso­la­tion is linked to changes in brain struc­ture and cog­ni­tion – the men­tal process of acquir­ing knowl­edge – it even car­ries an increased risk of demen­tia in old­er adults.

There’s already a lot of evi­dence in sup­port of the social brain hypoth­e­sis. One study mapped the brain regions asso­ci­at­ed with social inter­ac­tion in approx­i­mate­ly 7,000 peo­ple. It showed that brain regions con­sis­tent­ly involved in diverse social inter­ac­tions are strong­ly linked to net­works that sup­port cog­ni­tion, includ­ing the default mode net­work (which is active when we are not focus­ing on the out­side world), the salience net­work (which helps us select what we pay atten­tion to), the sub­cor­ti­cal net­work (involved in mem­o­ry, emo­tion and moti­va­tion) and the cen­tral exec­u­tive net­work (which enables us to reg­u­late our emotions).

We want­ed to look more close­ly at how social iso­la­tion affects grey mat­ter – brain regions in the out­er lay­er of the brain, con­sist­ing of neu­rons. We, there­fore, inves­ti­gat­ed data from near­ly 500,000 peo­ple from the UK Biobank, with a mean age of 57. Peo­ple were clas­si­fied as social­ly iso­lat­ed if they were liv­ing alone, had social con­tact less than month­ly and par­tic­i­pat­ed in social activ­i­ties less than weekly.

Our study also includ­ed neu­roimag­ing (MRI) data from approx­i­mate­ly 32,000 peo­ple. This showed that social­ly iso­lat­ed peo­ple had poor­er cog­ni­tion, includ­ing in mem­o­ry and reac­tion time, and low­er vol­ume of grey mat­ter in many parts of the brain. These areas includ­ed the tem­po­ral region (which process­es sounds and helps encode mem­o­ry), the frontal lobe (which is involved in atten­tion, plan­ning and com­plex cog­ni­tive tasks) and the hip­pocam­pus – a key area involved in learn­ing and mem­o­ry, which is typ­i­cal­ly dis­rupt­ed ear­ly in Alzheimer’s disease.

We also found a link between the low­er grey mat­ter vol­umes and spe­cif­ic genet­ic process­es that are involved in Alzheimer’s disease.

There were fol­low-ups with par­tic­i­pants 12 years lat­er. This showed that those who were social­ly iso­lat­ed, but not lone­ly, had a 26% increased risk of dementia.

Context and brain mechanisms:

Social iso­la­tion needs to be exam­ined in more detail in future stud­ies to deter­mine the exact mech­a­nisms behind its pro­found effects on our brains. But it is clear that, if you are iso­lat­ed, you may be suf­fer­ing from chron­ic stress. This in turn has a major impact on your brain, and also on your phys­i­cal health.

Anoth­er fac­tor may be that if we don’t use cer­tain brain areas, we lose some of their func­tion. A study with taxi dri­vers showed that the more they mem­o­rised routes and address­es, the more the vol­ume of the hip­pocam­pus increased. It is pos­si­ble that if we don’t reg­u­lar­ly engage in social dis­cus­sion, for exam­ple, our use of lan­guage and oth­er cog­ni­tive process­es, such as atten­tion and mem­o­ry, will diminish.

This may affect our abil­i­ty to do many com­plex cog­ni­tive tasks – mem­o­ry and atten­tion are cru­cial to com­plex cog­ni­tive think­ing in general.

Building cognitive reserve via social interaction:

We know that a strong set of think­ing abil­i­ties through­out life, called “cog­ni­tive reserve”, can be built up through keep­ing your brain active. A good way to do this is by learn­ing new things, such as anoth­er lan­guage or a musi­cal instru­ment. Cog­ni­tive reserve has been shown to ame­lio­rate the course and sever­i­ty of age­ing. For exam­ple, it can pro­tect against a num­ber of ill­ness­es or men­tal health dis­or­ders, includ­ing forms of demen­tia, schiz­o­phre­nia and depres­sion, espe­cial­ly fol­low­ing trau­mat­ic brain injury.

There are also lifestyle ele­ments that can improve your cog­ni­tion and well­be­ing, which include a healthy diet and exer­cise. For Alzheimer’s dis­ease, there are a few phar­ma­co­log­i­cal treat­ments, but the effi­ca­cy of these need to be improved and side effects need to be reduced. There is hope that in the future there will be bet­ter treat­ments for age­ing and demen­tia. One avenue of inquiry in this regard is exoge­nous ketones — an alter­na­tive ener­gy source to glu­cose – which can be ingest­ed via nutri­tion­al supplements.

But as our study shows, tack­ling social iso­la­tion could also help, par­tic­u­lar­ly in old age. Health author­i­ties should do more to check on who is iso­lat­ed and arrange social activ­i­ties to help them.

When peo­ple are not in a posi­tion to inter­act in per­son, tech­nol­o­gy may pro­vide a sub­sti­tute. How­ev­er, this may be more applic­a­ble to younger gen­er­a­tions who are famil­iar with using tech­nol­o­gy to com­mu­ni­cate. But with train­ing, it may also be effec­tive in reduc­ing social iso­la­tion in old­er adults.

Social inter­ac­tion is huge­ly impor­tant. One study found that the size of our social group is actu­al­ly asso­ci­at­ed with the vol­ume of the orbitofrontal cor­tex (involved in social cog­ni­tion and emotion).

But how many friends do we need? Researchers often refer to “Dunbar’s num­ber” to describe the size of social groups, find­ing that we are not able to main­tain more than 150 rela­tion­ships and only typ­i­cal­ly man­age five close rela­tion­ships. How­ev­er, there are some reports which sug­gest a lack of empir­i­cal evi­dence sur­round­ing Dunbar’s num­ber and fur­ther research into the opti­mal size of social groups is required.

It is hard to argue with the fact that humans are social ani­mals and gain enjoy­ment from con­nect­ing with oth­ers, what­ev­er age we are. But, as we are increas­ing­ly uncov­er­ing, it also cru­cial for the health of our cognition.

Bar­bara Jacque­lyn Sahakian is a Pro­fes­sor of Clin­i­cal Neu­ropsy­chol­o­gy at Uni­ver­si­ty of Cam­bridge. Chris­telle Lan­g­ley is a Post­doc Research Asso­ciate at Uni­ver­si­ty of Cam­bridge. Chun Shen is a Post­doc research fel­low at Fudan Uni­ver­si­ty. Jian­feng Feng is a Pro­fes­sor of Sci­ence and Tech­nol­o­gy for Brain-Inspired Intel­li­gence at Fudan Uni­ver­si­ty. This arti­cle was orig­i­nal­ly pub­lished on The Con­ver­sa­tion.

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