A central mechanism enhances pain perception of noxious thermal stimulus changes.

Pain perception temporarily exaggerates abrupt thermal stimulus changes revealing a mechanism for nociceptive temporal contrast enhancement (TCE). Although the mechanism is unknown, a non-linear model with perceptual feedback accurately simulates the phenomenon. Here we test if a mechanism in the central nervous system underlies thermal TCE. Our model successfully predicted an optimal stimulus, incorporating a transient temperature offset (step-up/step-down), with maximal TCE, resulting in psychophysically verified large decrements in pain response ("offset-analgesia"; mean analgesia: 85%, n = 20 subjects). Next, this stimulus was delivered using two thermodes, one delivering the longer duration baseline temperature pulse and the other superimposing a short higher temperature pulse. The two stimuli were applied simultaneously either near or far on the same arm, or on opposite arms. Spatial separation across multiple peripheral receptive fields ensures the composite stimulus timecourse is first reconstituted in the central nervous system. Following ipsilateral stimulus cessation on the high temperature thermode, but before cessation of the low temperature stimulus properties of TCE were observed both for individual subjects and in group-mean responses. This demonstrates a central integration mechanism is sufficient to evoke painful thermal TCE, an essential step in transforming transient afferent nociceptive signals into a stable pain perception.

Eye movements during emotion recognition in faces.

When distinguishing whether a face displays a certain emotion, some regions of the face may contain more useful information than others. Here we ask whether people differentially attend to distinct regions of a face when judging different emotions. Experiment 1 measured eye movements while participants discriminated between emotional (joy, anger, fear, sadness, shame, and disgust) and neutral facial expressions. Participant eye movements primarily fell in five distinct regions (eyes, upper nose, lower nose, upper lip, nasion). Distinct fixation patterns emerged for each emotion, such as a focus on the lips for joyful faces and a focus on the eyes for sad faces. These patterns were strongest for emotional faces but were still present when viewers sought evidence of emotion within neutral faces, indicating a goal-driven influence on eye-gaze patterns. Experiment 2 verified that these fixation patterns tended to reflect attention to the most diagnostic regions of the face for each emotion. Eye movements appear to follow both stimulus-driven and goal-driven perceptual strategies when decoding emotional information from a face.

Differential responses in the fusiform region to same-race and other-race faces.

Many studies have shown that people remember faces of their own race better than faces of other races. We investigated the neural substrates of same-race memory superiority using functional MRI (fMRI). European-American (EA) and African-American (AA) males underwent fMRI while they viewed photographs of AA males, EA males and objects under intentional encoding conditions. Recognition memory was superior for same-race versus other-race faces. Individually defined areas in the fusiform region that responded preferentially to faces had greater response to same-race versus other-race faces. Across both groups, memory differences between same-race and other-race faces correlated with activation in left fusiform cortex and right parahippocampal and hippocampal areas. These results suggest that differential activation in fusiform regions contributes to same-race memory superiority.