Men in love show more activity in the visual part of the brain, while women in love show more activity in the part of the brain that governs memory. Scientists speculate that men have to size up a woman visually to see if she can bear babies, while women have to remember aspects of man's behavior to determine if he would be an adequate provider.
Brains in love and brains in lust are not identical. Erotic photos activate the hypothalamus (which controls hunger and thirst) and the amygada (arousal) areas of the brain. Love activates areas of the brain with a high concentration of receptors for dopamine (associated with euphoria, craving, and addiction) and its relative, norepinephrine.
High levels of testosterone may suppress oxytocin and vasopressin (chemicals associated with attachment love), which may explain why men with higher testosterone levels tend to marry less often, be more abusive in their marriage, and divorce more. When a man holds a baby, his testosterone goes down, perhaps as a result of increased oxytocin and vasopressin.
Women often feel loved when talking face to face with their partner; men, on the other hand, often feel emotionally close when they work, play, or talk side by side.