After spending 14 frigid months in Antarctica, nine expeditioners left the continent with slightly smaller brains, according to a new study.
A team of researchers scanned the expeditioners' brains before and after the journey and found that certain structures in the organ had shrunk during the trip. In particular, a brain structure critical for learning and memory called the hippocampus had lost significant volume. The results, published today (Dec. 4) in The New England Journal of Medicine, suggest that the expeditioners may have missed out on much-needed brain stimulation by living and working in an isolated research station out on the polar ice, with only a few select people and for months on end.
The brain shrinkage may also undermine the expeditioners' ability to process emotions and interact with others, because the hippocampus is "key" to those cognitive abilities, co-author Alexander Stahn, a space medicine researcher at the Charité – Universitätsmedizin Berlin and assistant professor of medical science in psychiatry at the University of Pennsylvania, told Live Science in an email.
The brain changes seen in the Antarctic team echo similar observations made in rodents, which suggest that prolonged periods of social isolation blunt the brain's ability to build new neurons. Living in a "monotonous" environment, a place that rarely changes and contains few interesting objects or rooms to explore, seems to prompt changes in rodents' brains that resemble those seen in the expeditioners, particularly in the hippocampus. As one of the few brain regions to generate neurons into adulthood, the hippocampus continually rewires our neural circuitry as we learn and gain new memories, according to BrainFacts.org.
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Although the rodent brain seems to rely on environmental stimulation to sustain the hippocampus, less is known about the effects of isolation and monotony on the human brain. Stahn and his co-authors thought that a remote research station at the South Pole might serve as the perfect laboratory to investigate. Stahn primarily studies how the brain might change during long-term space travel, but Antarctica allowed him to examine those effects a bit closer to home, he said.
"It can be considered an excellent space analogue to assess the effects of prolonged isolation and confinement," he said.
The polar research station in question, called the Neumayer Station III, stands on the Ekström Ice Shelf near the Weddell Sea and houses nine people through the winter months, according to the Alfred Wegener Institute, which runs the station. The building itself contains most of the team's workspaces, common areas and supply rooms, looming above the snow-covered ice shelf on 16 hydraulic struts. Surrounded by bitter-cold wilderness, the station certainly fits the textbook definition of "isolated."
Before the expeditioners hunkered down for the Antarctic winter, Stahn and his co-authors scanned the subjects' brains via magnetic resonance imaging (MRI), which uses a strong magnetic field and radio waves to capture structural images of the brain. For medical reasons, one of the expeditioners could not undergo MRI, but the authors did measure internal levels of a protein called brain-derived neurotrophic factor (BDNF) for all nine team members. The BDNF protein supports the growth of new neurons and enables the budding cells to survive; without BDNF, the hippocampus cannot forge new neural connections.
The authors tested the expeditioners' BDNF levels and cognitive performance throughout the expedition, scanning their brains again after the team returned home. Researchers also drew the same measurements from nine healthy participants who did not go on the expedition.
Sure enough, the expeditioners lost more hippocampal volume and BDNF during their 14 months at the South Pole than the group who stayed home.
In particular, a region of the hippocampus called the dentate gyrus dipped significantly in the eight expeditioners who underwent MRI. This region serves as the hotbed of neurogenesis within the hippocampus and records memories of events, according to BrainFacts.org. On average, each expeditioner's dentate gyrus shrunk by about 4% to 10% during their stay at the research station.
Expeditioners with greater volume loss in the dentate gyrus also performed worse on tests of spatial processing and selective attention, compared with their scores before the expedition. Other areas of expeditioners brains' also seemed to shrink during the trip, including several spots on the cerebral cortex (the wrinkled outer layer of the brain); these spots were the left parahippocampal gyrus, right dorsolateral prefrontal cortex and left orbitofrontal cortex.
A quarter of the way through the expedition, the expeditioners' BDNF levels had already fallen from their baseline levels, and they eventually decreased by about 45%, on average. These levels remained low even 1.5 months after the team returned home. Greater reductions in BDNF levels correlated with greater volume loss in the dentate gyrus from before the expedition to afterward, the study said.
Because their study included only nine people, the authors stressed that their "data should be interpreted with caution." Based on their research alone, the authors cannot determine which elements of the expedition constituted social or environmental deprivation, specifically, they noted. Nonetheless, the researchers said, the results hint that prolonged isolation may deplete the human brain of BDNF, alter the structure of the hippocampus and undermine important cognitive functions like memory.
The researchers are currently investigating several possible ways to preventive this brain shrinkage, "such as specific physical exercise routines and virtual reality to augment sensory stimulation," Stahn said. Theoretically, if findings from rodent studies hold true in humans, "enriching" a person's environment with new items and activities could shield the hippocampus from shrinkage, the authors said.
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Originally published on Live Science.