If love is said to come from the heart, what about hate? Along with music, religion, irony and a host of other complex concepts, researchers are on the hunt for the neurological underpinnings of hatred. Functional magnetic resonance imaging (fMRI) has begun to reveal how the strong emotion starts to emerge in the brain.

Neurobiologist Semir Zeki, of University College London's Laboratory of Neurobiology, led a study last year that scanned the brains of 17 adults as they gazed at images of a person they professed to hate. Across the board, areas in the medial frontal gyrus, right putamen, premotor cortex and medial insula activated. Parts of this so-called "hate circuit," the researchers noted, are also involved in initiating aggressive behavior, but feelings of aggression itself—as well as anger, danger and fear—show different patterns in the brain than hatred does.

Certainly loathing can spring from positive feelings, such as romantic love (in the guise of a former partner or perceived rival). But love seems to deactivate areas traditionally associated with judgment, whereas hatred activates areas in the frontal cortex that may be involved in evaluating another person and predicting their behavior.

Some commonalities with love, however, are striking, the study authors note. The areas of the putamen and insula that are activated by individual hate are the same as those for romantic love. "This linkage may account for why love and hate are so closely linked to each other in life," they wrote in the October 2008 PLoS ONE.

This initial study, however, does not have everyone convinced that researchers have uncovered the neurological root of hatred. "This is really early in the game," says Scott Huettel, an associate professor of psychology and neuroscience at Duke University who was not involved in the study. Other emotions, such as happiness and sadness, are much better understood, he says: "Even things like regret have some pretty clear neural coordinates."

The next step, Huettel points out, will be to conduct more research on clearly defined aspects and types of hatred—including group hate rather than that aimed at individuals—then test them across several different situations. It will also be important, he notes, to look for cases in which parts of the brain have been impaired and emotional tendencies have changed. "Once you show the positive activation and impairment when the brain region is damaged you have good evidence that you have at least part of the circuit," he says.

What purpose the emotion of hate serves is also still up for conjecture. Although some argue that the feeling has an evolutionary advantage—it might help an individual decide whom to confront or scorn—Huettel notes that, like pinpointing a dedicated neural circuit, it is all just "educated guesses at this point."

Don't you just hate that?