A study utilizing magnetic resonance imaging (MRI) sought to examine the brain functioning of cohabitating and married women when facing stress. Researchers administered to both sets of women a mild electronic shock on the ankle. For support, the women had three choices: hold the hand of their partners, hold the hand of a stranger, or face the shock alone. When a married woman held the hand of her spouse, she registered a deep sense of calm in the hypothalamus region of her brain as she prepared for the shock. Conversely, cohabitating women holding the hand of the live-in partner registered little to no calm.

What surprised researchers is that while both sets of women stated that they felt commitment from the partners, the cohabitating women recorded the same level of calm as those holding the hand of a stranger. Researchers speculate that while cohabitating women say they feel commitment from the partner, doubt resides in the deepest part of their brains.