Scientists know that running induces the production of new neurons in rodent brains. Elizabeth Gould and colleagues at Princeton University report that this benefit is wiped out when animals are housed individually, a situation she likens to “solitary confinement” for humans.
As seen previously, group-housed animals had significantly increased levels of neurogenesis in their brains after just 12 days of running, relative to their group-housed companions who did not have access to a running wheel. Meanwhile, animals that were housed individually had the same low level of cell proliferation as the group-housed controls, regardless of whether the solitary animals had access to a running wheel.
When an additional stressor was added to the mix, such as daily handling by the researchers or brief cold-water swims, the isolated runners actually had less cell growth than non-runners in either housing situation. Thus the beneficial effects of exercise not only were dampened, but actually were reversed in the presence of excess stress and social isolation.
Gould’s group found that stress hormones were elevated in all runners for a brief period of time when they were most active, which seems logical because running is physiologically stressful. The isolated runners, though, showed elevated stress hormones during other parts of their day as well as during active periods. “Positive social interaction can buffer the physiological effects of stress,” Gould concludes. Although she is cautious about extrapolating too directly to humans, she expects the benefits of good social connections may have a physiological impact on stress in us as well.