An excerpt from Eric Kandel's The Age of Insight, in Scientific American:
Semir Zeki of University College London found that the orbitofrontal region is also activated in response to other, subtly pleasurable images that we interpret as beautiful. Zeki conducted a study in which he first asked volunteers to examine a large number of portraits, landscapes, and still lifes. He then had the volunteers classify the art, irrespective of category, on the basis of whether they found the painting beautiful or ugly. Zeki imaged the volunteers’ brains as they looked at the paintings and found that all of the portraits, landscapes, and still lifes, regardless of whether the viewer saw them as beautiful or ugly, lit up the orbitofrontal, prefrontal, and motor regions of the cortex. Interestingly, however, the pictures ranked most beautiful activated the orbitofrontal region most and the motor region least, whereas the pictures ranked ugliest activated the orbitofrontal region least and the motor region most. The activation of the motor region of the cortex suggests to Zeki that emotionally charged stimuli mobilize the motor system to be prepared to take action to get away from the stimulus in the case of ugliness or threat and toward the stimulus in the case of beauty or pleasure. Indeed, as we know, fearful faces also activate the motor region of the cortex.
Beauty does not occupy a different area of the brain than ugliness. Both are part of a continuum representing the values the brain attributes to them, and both are encoded by relative changes in activity in the same areas of the brain. This is consistent with the idea that positive and negative emotions lie on a continuum and call on the same neural circuitry. Thus, the amygdala, commonly associated with fear, is also a regulator of happiness.
For every evaluation of emotion, from happiness to misery, we use the same fundamental neural circuitry. In the case of art, we evaluate a portrait’s potential for providing new insights into another person’s psychological state. This discovery, by Ray Dolan and his colleagues at University College London, was based on a set of studies in which volunteers viewed faces whose expression of sadness, fear, disgust, or happiness was gradually changed from low to high intensity.