Poets and scientists explain love differently; I'm a scientist. Only during the past few decades have scientists developed the tools necessary to ask the right questions. Psychologists frequently explain love according to the theory of attachment: Animals develop an emotional attachment with their primary caregivers whom they depend on for their survival. The emotional strategy of developing feelings of maternal love ultimately supports a lifelong sequence of relationships with siblings, mating partners, and their offspring that repeats across generations.

The neurochemistry of love

Animal and human studies have implicated important roles in two neurotransmitter systems, oxytocin and dopamine. Oxytocin was once dubbed the molecule of love and healing; it is now seen as so much more. Intranasal administration of oxytocin produces feelings of trust, group affiliation, reduced social anxiety, and cooperation. In addition, it also promotes aggression toward threatening out-group rivals (those who might threaten members of the family group) and may, according to recent theories, underlie aspects of racism. Oxytocin also stimulates bonding between mother and child. There is no evidence that oxytocin has an aphrodisiac effect.

Dopamine plays a different supporting role. Dopamine neurons within a small region in the brainstem (called the VTA) project up into the center of each cerebral hemisphere to control motivation, movement towards rewarding stimuli, and reward-seeking behaviors. Scientists speculate that from an evolutionary perspective, these dopamine neurons are involved in directing our behaviors toward specific goals that provide some type of reward, including maternal attachment and passionate love. Survival is greatly supported by developing attachments with others.

An essential part of developing attachment is motivation when the combined actions of dopamine and oxytocin come into play. Their role in attachment is supported by the fact that losing a partner leads to suppressing oxytocin's communication with dopamine within the brain's reward center. The loss of a loved one leads to a life without the ability to experience rewards, a type of anhedonia seen with anti-psychotic medications that block the actions of dopamine in these identical brain regions.

Where is the love?

Functional magnetic resonance imaging studies have attempted to answer this question. Their studies have shown that specific brain regions that depend on dopamine input from the brainstem and contain both dopamine and oxytocin receptors are activated during the expression of both maternal and passionate love. These regions include the putamen, globus pallidus, and caudate nucleus. (For more details on the function of these brain regions, read my book The Brain.)

In addition, both kinds of love turned off activity within the amygdala and mesial prefrontal cortex, which regulate negative emotions. Other fMRI studies found that passionate love recruited similar regions, as well as the anterior cingulate gyrus. Overall, the evidence provides a consistent conclusion: Maternal and passionate love activates brain regions full of dopamine and oxytocin receptors.

These studies suggest maternal and passionate love share a common evolutionary origin and neurobiological mechanisms. A mother's love teaches a child the importance of emotional connection with reciprocity. A child then learns to trust others, leading to emotional intimacy in their future relationships that enhances the survival and procreation of the species.