- Researchers have found an association between social isolation and lower brain volume.
- A loss of brain volume suggests neurodegeneration that may result in dementia or Alzheimer’s disease.
- While establishing a causal link between social isolation and brain-volume loss was beyond the scope of this study, other research supports this possibility.
- In addition, previous studies have linked social isolation to cognitive loss and dementia.
A new study finds an association between social isolation and a reduction in brain volume among older people. Brain volume loss is considered a sign of neurodegeneration due to cell death and atrophy.
Among the study’s participants, MRI scans showed that the white and gray brain matter of those with the least social contact occupied 67.3% of the available intracranial volume. Those with the highest amount of social contact occupied 67.8%.
The correspondence between social isolation and dementia does not indicate that one causes the other. However, it may offer a clue as to what causes dementia.
The results of this study appear in Neurology.
The researchers — from Kyushu University in Fukuoka, Japan — found that a reduction in brain volume affected areas linked to memory and dementia, such as the hippocampus and amygdala. The hippocampus is a brain region believed to be associated with Alzheimer’s disease.
The temporal lobe, occipital lobe, and cingulum were also reduced. The researchers found that depression was a contributing factor but only accounted for 15% to 29% of the connection between social isolation and brain volumes.
The scans also revealed that the most socially isolated people had a higher amount of white matter lesions that indicate brain damage.
White matter lesions constituted 0.30% of intracranial volume for those people and 0.26% for people who were not as socially isolated.
The study involved 8,896 dementia-free people with an average age of 73 living in a community setting in Japan.
Prof. Barbara Sahakian, a specialist in Alzheimer’s disease from the University of Cambridge in the United Kingdom, who was not involved in this study, has also published related research on the link between brain volume and cognitive function.
She explained to Medical News Today that “[t]he impact of social stressor on hippocampal morphology has been well documented.” She also reported that the amygdala “plays an essential role in emotional processing, and was relevant to social network size.”
Dr. Roseanne Freak-Poli — an epidemiologist from Monash University in Australia, also not involved in the current research — agreed with Prof. Sahakian on the link between brain volume and cognition.
She told us that “there are
Prof. Sahakian further pointed to animal studies that have “suggested that isolation affected cognition via altering the excitatory and inhibitory synaptic density in the hippocampus, and social interaction rescued memory deficit by increasing hippocampal neurogenesis.”
In addition, said Prof. Sahakian, their own study “showed that socially isolated people had poorer cognition, including in memory and reaction time, and a lower volume of grey matter in many parts of the brain.”
“We also found a link between the lower grey matter volumes and specific genetic processes that are involved in Alzheimer’s disease,” she noted.
Saying that previous research has viewed cognitive function through the administering of verbal tests, Dr. Freak-Poli noted:
“What this paper adds is assessment of brain volumes through scanned measurements, which are linked to cognitive function. This paper gives an understanding of how the structure of the brain may be negatively influenced by social isolation.”
However, added Dr. Freak-Poli, “It is important to acknowledge that other factors associated with social isolation may also enact a reduction in brain volume.”
Prof. Sahakian’s research also suggested a possible mechanism: “We found a link between the lower grey matter volumes and specific genetic processes that are involved in Alzheimer’s disease.”
Prof. Sahakian explained how and why social isolation can impact a person’s cognitive abilities:
“Our brains require social interaction for development, in terms of honing our social skills, such as empathy and the ability to understand other people. In addition, interacting with others promotes activation in social brain areas, as well as providing feelings of well-being and enjoyment.”
Prof. Sahakian suggested that in learning to interact with family, friends, and others early in life, we create the building blocks for other forms of cognition. She said that when we have no opportunity to practice our social skills, they can deteriorate, potentially weakening our whole cognitive structure.
“Two systematic reviews [one in
In her research, Prof. Sahakian found that gray matter volumes partly mediated the link between social isolation and cognitive function but that “this is not evidence of a causal relationship.”
Prof. Sahakian cited the “brain reserve hypothesis of dementia.” It proposes that a larger brain volume provides more neural matter with which to maintain cognitive function and fend off pathology.
“Our findings implicated that isolation, as a social stressor, might reduce available brain reserve to accelerate cognitive decline, and finally lead to increased risk of dementia.”
Dr. Freak-Poli recommended viewing social isolation and dementia as a two-way street. She considered it more likely that a lack of social interaction may affect the brain, perhaps leading to [a] loss of cognitive function.
Going the other direction, though, once cognitive loss begins to occur, people may find social contact too difficult, or even embarrassing, as they have trouble remembering previous conversations.
“Withdrawing from social contact may then accelerate their declining cognitive function. Hence, a downward spiral,” said Dr. Freak-Poli.