There is a strong link between certain psychological factors, such as depression and social isolation, and heart disease. Moreover, people who survive cardiac arrest and cardiopulmonary resuscitation are predisposed to develop a host of chronic physiological and psychiatric conditions due to neuronal damage caused by the temporary lack of blood flow to the brain. Now, a study with mice has shown that social interaction modulates some of the physiological and behavioral responses to a heart attack. Importantly, these results suggest that social isolation exacerbates certain responses to cardiac arrest (Proc. Natl. Acad. Sci. USA 107, 16342–16347; 201010.1073/pnas.1007583107).

In this study, Greg Norman and colleagues at Ohio State University in Columbus housed male mice either alone or with a female mouse (whose ovaries had been removed). The research team implanted an electrocardiograph-like device into each male mouse. This device recorded and transmitted data, such as heart rate variability. After 2 weeks of the study, the researchers surgically induced heart attacks in some of the male mice and then resuscitated these mice. Other male mice underwent a sham control surgery. The researchers then analyzed tissue samples taken from mice 24 hours, 3 days or 7 days after surgery.

Within 24 hours after cardiac arrest, mice showed damage to the regulation of their heart rates, though the mice who lived with a female mouse showed significantly less damage than did the mice who lived alone. Specifically, the mice who lived with a partner had half as much neuronal cell death in the hippocampus region of the brain than did the mice who lived alone. The socially isolated mice appeared to show more depressive-like behavior as well. When placed in water, socially housed mice spent more time swimming and singly housed mice spent more time floating, which is considered a depressive symptom.

Within 3 days after cardiac arrest, the socially isolated mice had higher levels of the stress hormone corticosterone than did socially housed mice. While all mice recovering from heart attacks showed evidence of increased pro-inflammatory chemicals, the socially isolated mice appeared to have even higher levels of these chemicals than did the mice with partners. These results show that “[s]ocial isolation hits cardiac arrest victims from multiple angles,” said Norman in a press release. “It is involved in results for cell death, inflammation and a variety of behavioral and physiological measures. You really see the ability of social interaction to influence recovery.”