The link between mother and child during pregnancy is perhaps the closest that two humans can ever be linked, but after childbirth they become two separate individuals — or do they? New research suggests that the connection between mother and child may be much stronger than previously thought. The study, which was published recently in PLOS ONE, reveals that male cells have been found in the brains of women, sometimes decades after a woman had given birth. The findings could have broad implications, ranging from disease prevention to identifying immune disorders.