Brain Changes in Response to Long Antarctic Expeditions

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Studies in animals have shown that exposure to environmental monotony and social isolation have deleterious effects on the brain, particularly in reducing the generation of new neurons in the dentate gyrus of the hippocampus (x).^1-3 Whether stressors associated with prolonged isolation lead to similar impairments in brain plasticity in humans is not known. To evaluate the effects of physical and social deprivation on the hippocampus, we conducted a study involving persons who had participated in polar expeditions, which are characterized by environmental monotony and prolonged physical and social isolation.⁴

Our study involved nine polar expeditioners (five men and four women) who lived in Antarctica for 14 months at the German Neumayer III station. 

Ett s.k. QSL-kort visande att det finns en radioamatörstation på forskningsstationen (DP0GVN)

We obtained high-resolution T1- and T2-weighted magnetic resonance imaging (MRI) data (Siemens Tim Trio 3T scanner) on eight expeditioners. One of the nine expeditioners could not undergo MRI (Magnetisk resonanstomografi (MRI , ofta felaktigt benämnt magnetröntgen) for medical reasons, and only the brain-derived neurotrophic factor (BDNF(se:https://sv.wikipedia.org/wiki/Brain derived_neurotrophic_factor ) measurements for that expeditioner were used in the analysis. Imaging and other data were obtained before and after the mission to study changes in the volume of subsections of the hippocampus and of whole-brain gray matter. We analyzed cognitive performance and BDNF concentrations in all nine crew members before, during, and after the expedition. To account for biologic variation and effects of aging on brain changes, we obtained longitudinal data from nine controls who were matched with the expeditioners for age, sex, and initial hippocampal volume (Table S1 in the Supplementary Appendix, available with the full text of this letter at NEJM.org). Detailed methods and additional analyses are provided in the Supplementary Appendix.

Figure 1.

Changes in Brain Volume and Brain-Derived Neurotrophic Factor (BDNF) Concentrations in Antarctic Expeditioners.

In the eight expeditioners who underwent MRI, the reductions in the hippocampal volume of the dentate gyrus from before to after the expedition were greater than the changes over 14 months in the controls (mean [±SE] decrease in volume in the expedition group, 32±13 mm³, equivalent to a 7.2±3% reduction in volume). The volume of other hippocampal regions (the cornu ammonis subfields 1 through 3, subiculum, entorhinal cortex, and parahippocampal gyrus) also decreased, but these changes did not reach statistical significance (Figure 1A and Table S2). Whole-brain imaging in the expeditioners showed mean (±SE) decreases in gray-matter volume in the left parahippocampal gyrus (3.84±0.72%), right dorsolateral prefrontal cortex (3.33±0.48%), and left orbitofrontal cortex (2.99±0.25%) (Figure 1B).

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 (mean reduction, 11±1.5 ng per milliliter, 45.0±4.9%) (Figure 1C). Reductions in BDNF concentrations from before to after the expedition were associated with decreases in dentate gyrus volume (R²=0.47) (Fig. S2). The reductions in dentate gyrus volume were also associated with lower cognitive performance in tests of spatial processing (R²=0.87) and selective attention (Stroop Incongruent Task) (R²=0.82) (Fig. S3), but there was no decrease in performance in other cognitive tests such as the Digit Symbol Substitution Test and the Stroop Congruent Task, as noted in the Supplementary Appendix.

Variations in physical and social environments influence hippocampal plasticity.⁵ The characteristics of the expedition (i.e., the restriction to a single living and work space, limits on the exposure to varying and complex hippocampus-relevant stimuli, and social interactions that were limited to a small group of people for a prolonged period of time) may have mediated the reductions in BDNF concentrations and related volumetric brain changes. 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.^1-3 Only nine persons were involved in our study, and our data should be interpreted with caution since we cannot determine which elements of the expedition constituted social or environmental deprivation. Other unmeasured or undetected aspects of the experience may also have been involved in the changes observed. Data to determine the mechanisms of the effects of environmental deprivation and social isolation on brain plasticity in humans are lacking.

Alexander C. Stahn, Ph.D.
Hanns-Christian Gunga, M.D.
Charité–Universitätsmedizin Berlin, Berlin, Germany
alexander.stahn@charite.de

Eberhard Kohlberg, M.D.
Alfred-Wegener-Institut, Bremerhaven, Germany

Jürgen Gallinat, M.D.
University Medical Center Hamburg–Eppendorf, Hamburg, Germany

David F. Dinges, Ph.D.
University of Pennsylvania, Philadelphia, PA

Simone Kühn, Ph.D.
Max Planck Institute for Human Development, Berlin, Germany

(x) Hippocampus spelar en stor roll för konsolidering av information från korttidsminnet till långtidsminnet. Hippocampus möjliggör bland annat vår förmåga att orientera oss rumsligen, särskilt när det gäller att ta sig fram och tillbaka i ett tidigare okänt område. Inga minnen lagras i hippocampus, hippocampus agerar snarare som en kopplingsstation som förbinder associationsbanor mellan de olika delarna av hjärnan.^[1]

Namnet kommer från grekiska  hippos, 'häst' och kampos, 'sjömonster', vilket tillsammans blir  "Sjöhäst", och syftar på organets/strukturens form och utseende.

(xx)Konsolidering (minne) – processer i hjärnan som gör att information överförs från korttidsminnet till långtidsminnet

A CLOSE-UP VIEW OF THE HIPPOCAMPAL FORMATION, WHICH INCLUDES THE DENTATE GYRUS.
(Från nätet)