Prolonged physical and social isolation can lead to potentially harmful changes in brain volume and cognition, find German researchers who studied people undertaking long polar expeditions.

In a letter to the NEJM, Alexander C Stahn and colleagues from the Charité–Universitätsmedizin Berlin, Germany, said studies in animals had shown that exposure to environmental monotony and social isolation have deleterious effects on the brain, but it was unknown whether this was the case in humans.

They therefore analysed brain imaging, cognitive performance and brain-derived neurotrophic factor (BDNF) concentrations in polar expeditioners before, during, and after a 14 month long expedition to Antarctica.

The findings were compared with matched controls in order to account for biologic variation as well as the effects of aging on brain changes.

Of the 8 expeditioners who underwent MRI, reductions in hippocampal volume of the dentate gyrus from before to after the expedition were greater than the changes over 14 months in the controls, with the decrease in the expedition group equivalent to a 7.2%±3% reduction in brain volume.

Whole-brain imaging in the expeditioners also showed decreases in gray-matter volume in the left parahippocampal gyrus, right dorsolateral prefrontal cortex and left orbitofrontal cortex.

Furthermore, after the first quarter of the expedition, the serum BDNF concentrations were lower than the concentrations before the expedition and had not recovered at 1.5 months after the end of the expedition.

Reductions in BDNF concentrations from before to after the expedition were associated with decreases in dentate gyrus volume and were associated with lower cognitive performance in tests of spatial processing and selective attention.

“The vulnerability of the dentate gyrus to environmental deprivation, as compared with the vulnerability of other hippocampal subfields, is similar to findings from studies in animals, suggesting possible links among hippocampal neurogenesis, stress-induced behavioral changes, and environmental deprivation,” the researchers concluded.

They noted that as there were only nine people involved in the study the data should be interpreted with caution as it was difficult to determine which elements of the expedition constituted social or environmental deprivation.