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This question originally appeared on Quora. Answer by Yohan John, PhD in cognitive neural systems from Boston University.

We can try! Social neuroscience is the sub-field of neuroscience that attempts to understand the particularly social behaviors that humans exhibit. Love may be the best example of this sort of behavior.

In order to study a neural phenomenon in humans, we first need to have what is known as an "operational" definition of that phenomenon. A working definition of love needs to be made in terms of non-neural observables. We use this definition to determine whether a person loves someone or something. We might choose a combination of factors like elevated heart rate or smiling or pupil dilation. But these are indirect measures themselves. Ultimately we are better off using questionnaires: it's best to just ask a person who or what they love.

Once we have a working definition of love, we can begin to study it experimentally. We can record a person's neural signals while they are looking at a picture of a loved one. We might use fMRI, EEG, MEG, PET, or some other method. We could also use methods that track the levels of some neurochemical in the blood.

We can't just measure what happens in a person's nervous system when they are looking at a loved one. This measurement is meaningless unless we compare it with some baseline. So we also need to make measurements of a "non-love" or neutral state. These measurements are known as controls. By comparing our neural love patterns with our neural "meh" patterns, we can start to see what is neurally different about love compared with other mental states.

Using these kinds of techniques, we have collected various pieces of information. They don't really add up to a neural theory of love, but they are tentative steps in that direction. Here are a few examples from an article in Psychology Today: "What Neuroscience Tells Us About Being in Love."

  • Love seems to activate the ventral tegmental area, which contains neurons that release the neurotransmitter dopamine. Dopamine is not the "pleasure chemical," but it has been associated with reward, punishment, addiction, learning, novelty, surprise, salience, and other phenomena.
  • Love may cause a drop in serotonin levels. Serotonin is not the "bliss chemical." In fact, serotonin remains a very poorly understood neurotransmitter.
  • Love may cause reduced activity in the prefrontal cortex (PFC) and in the amygdala. The PFC is a large and multifaceted brain region that is involved in all sorts of things, including decision-making, cognition, attention, emotion, and planning. The amygdala is a crucial hub of the emotional system, and is particularly involved in fear processing.
  • Love may affect men's and women's brains differently. In men, the visual cortex may be relatively more activated by love. In women, the hippocampus — a key part of the brain's memory system — may be more activated by love.

Remember, these are just examples, and not an exhaustive survey of the literature. Also, note that I used words like "seems," and "may." This is because social neuroscience is perhaps the most tricky sub-field of neuroscience. Many research findings seem inconsistent with each other, and attempts to replicated them often fail. Moreover, we can't really confirm most of these findings in laboratory animals, since it will always be controversial to attribute complex human emotions to organisms that cannot speak for themselves. So take these points with a very large pinch of salt. Some of these neural "signatures" of love may actually be giving us an incorrect or incomplete picture. Everyone knows that love is complicated, so we should expect that it will be among the most difficult things to understand from a neural perspective.