2026 年 63 巻 3 号 p. 79-91
The human brain oscillates in harmony with frequency-specific subcomponents of several brain regions. The heart and brain are connected bi-directionally, and heart rate variability (HRV) may reflect the activity of the coordinating system, notably brain functional connectivity, including the default mode network (DMN). As shown herein, HRV may thus inform about humans’ mind, including the well-being (e.g., satisfaction). First, the VLF component (0.003–0.04 Hz) of HRV (VLF-HRV) in healthy subjects statistically decreased by 21.9% (n=18, p<0.00001) in association with appearance of the Northern Lights, and a graded decrease in VLF-HRV was validated depending on the degree of geomagnetic activity (p<0.05). Second, we confirmed 20 astronauts’ response to space in terms of their HRV endpoints. VLF-HRV decreased by 23.2% (n=20, p<0.001) in space, and a decrease in VLF-HRV was validated depending on the degree of adaptation to microgravity in space. i.e., extent of VLF-HRV decrease was 29.7% when visiting space in 9 sufficiently adapted astronauts (p<0.05), but 12.9% in 11 poorly adapted astronauts (N.S.). VLF-HRV is known as a powerful predictor of cardiovascular disease risk, whereas it was recently noted as a representative HRV index which inversely reflects a sense of deeply impressed satisfaction related to the brain’s DMN activity. It could thus be said that an abrupt decrease in VLF-HRV could mean survival (strong happiness) or death (life threatening condition) depending on the circumstances, because from a viewpoint of functional brain’s neural networks, those outcomes are opposite sides of the same coin.
