Our experiences of the external events and objects that we encounter are colored by our internal subjective reactions to them; don rose-colored lenses and even the gloomiest day gives way to a sunny disposition. But how does the brain encode the affective value—positive or negative valence—of stimuli? Is there a common neural code for the joyful feeling roused by the sight of playful puppies and the aroma of a warm apple strudel?

Chikazoe et al. address this question on page 1114 of this issue by presenting volunteers with images that varied in terms of their visual complexity, level of animacy and subjective affect. Using patterns of activity measured with BOLD fMRI, the authors found that subjective affect (whether a stimulus was perceived as pleasing or unpleasant) was represented in the orbital frontal cortex (OFC), whereas visual complexity and animacy were represented in early visual and ventral temporal cortices, respectively. The more similar the images were rated on affect, the more closely the patterns of activity in the OFC matched each other irrespective of the exact visual features of the stimuli. This code was found to be intermingled in the same areas of the OFC, explaining why previous attempts to find specific regions for positive or negative valence have failed.

To see if this code applies to different types of sensory stimuli, the authors presented the same subjects with different tastes that varied in their affective qualities. Patterns of activity in the OFC represented the affective properties of the tastes independent of whether they were sweet, salty, bitter or sour, and pleasant or unpleasant tastes and images elicited similar patterns of activity.

To further demonstrate the commonality of this affective code, the authors decoded the affective experience of a subject by using the activity patterns of other subjects. The response to one stimulus predicted the response to similar stimuli in other people. This worked across modalities such that the reaction to a bad taste in some predicted the neural response to an unsightly image for others.

These results indicate that, in the OFC, the brain represents the valence of stimuli independent of their sensory attributes and forms a higher, abstract affective representation akin to other categories (such as animate or inanimate) in different brain regions. Thus, for the OFC, it's all the same whether a stimulus is made of sugar, spice or anything nice.