While humor typically involves a surprising discovery, not all discoveries are perceived as humorous or lead to a feeling of mirth. Is there a difference in the neural signature of humorous versus nonhumorous discovery? Subjects viewed drawings that were uninterpretable until a caption was presented that provided either: 1) a nonhumorous interpretation (or insight) of an object from an unusual or partial view (UV) or 2) a humorous interpretation (HU) of the image achieved by linking remote and unexpected concepts. fMRI activation elicited by the UV captions was a subset of that elicited by the humorous HU captions, with only the latter showing activity in the temporal poles and temporo-occipital junction (linking remote concepts), and medial prefrontal cortex (unexpected reward). Mirth may be a consequence of the linking of remote ideas producing high-and unexpected-activation in association and classical reward areas. We suggest that this process is mediated by opioid activity as part of a system rewarding attention to novel information.

Face recognition involves collaboration of a distributed network of neural correlates. However, how different attributes of faces are represented has remained unclear. We used functional magnetic resonance imaging-adaptation (fMRIa) to investigate the representation of viewpoint, expression, and identity of faces in the fusiform face area (FFA) and the occipital face area (OFA). In an event-related experiment, subjects viewed sequences of two faces and judged whether they depicted the same person. The images could vary in viewpoint, expression and/or identity. Critically, the physical similarity between view-changed and between expression-changed faces of the same person were matched by the Gabor-jet metric, a measure that predicts almost perfectly the effects of image similarity on face discrimination performance. In FFA, changes of identity produced the largest release from adaptation followed by changes of expression; but the release caused by changes of viewpoint was smaller and not reliable. OFA was sensitive only to changes in identity, even when image changes produced by identity variations were matched to those of expression and orientation. These results suggest that FFA is involved in the perception of both identity and expression of faces, a result contrary to the hypothesis of independent processing of changeable and invariant attributes of faces in the face-processing network.

Viewing a sequence of faces of two different people results in a greater Blood Oxygenation Level Dependent (BOLD) response in FFA compared to a sequence of identical faces. Changes in identity, however, necessarily involve changes in the image. Is the release from adaptation a result of a change in face identity, per se, or could it be an effect that would arise from any change in the image of a face? Subjects viewed a sequence of two faces that could be of the same or different person, and in the same or different orientation in depth. Critically, the physical similarity of view changes of the same person was scaled, by Gabor-jet differences, to be equivalent to that produced by an identity change. Both person and orientation changes produced equivalent releases from adaptation in FFA (relative to identical faces) suggesting that FFA is sensitive to the physical similarity of faces rather than to the individuals depicted in the images.

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