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

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.

To Learn More:

• The neu­ro­science behind why our brains will need time to adjust to ‘un-social distancing’
• Can you grow your hip­pocam­pus? Yes. Here’s how, and why it matters
• Three ways to pro­tect your men­tal health dur­ing –and after– COVID-19