Brain signatures of perceiving a smile: Time course and source localization

David Beltrán & Manuel G Calvo
In Human Brain Mapping

Facial happiness is consistently recognized faster than other expressions of emotion. In this study, to determine when and where in the brain such a recognition advantage develops, EEG activity during an expression categorization task was subjected to temporospatial PCA analysis and LAURA source localizations. Happy, angry, and neutral faces were presented either in whole or bottom-half format (with the mouth region visible). The comparison of part- versus whole-face conditions served to examine the role of the smile. Two neural signatures underlying the happy face advantage emerged. One peaked around 140 ms (left N140) and was source-located at the left IT cortex (MTG), with greater activity for happy versus non-happy faces in both whole and bottom-half face format. This suggests an enhanced perceptual encoding mechanism for salient smiles. The other peaked around 370 ms (P3b and N3) and was located at the right IT (FG) and dorsal cingulate (CC) cortices, with greater activity specifically for bottom-half happy versus non-happy faces. This suggests an enhanced recruitment of face-specific information to categorize (or reconstruct) facial happiness from diagnostic smiling mouths. Additional differential brain responses revealed a specific “anger effect,” with greater activity for angry versus non-angry expressions (right N170 and P230; right pSTS and IPL); and a coarse “emotion effect,” with greater activity for happy and angry versus neutral expressions (anterior P2 and posterior N170; vmPFC and right IFG). 

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Repeated exposure to meaningless pseudowords modulates LPC

Beatriz Bermúdez-Margaretto et al

In Brain Topography

Training readers to recognize pseudowords could decrease the processing differences between them and real words while clarifying the lexical acquisition processes. We analyze the effect of pseudoword repetition through the recording of EEG during a lexical decision task. Results showed a functional dissociation between two well-known ERP components: FN400 (Frontal N400, traditionally related to semantic processes) and LPC (Late Positive Complex, related to memory processes). On the one hand, FN400 was unaffected by pseudoword repetition and showed the typical lexicality effect. On the other hand, topographic and neural source analyses showed that LPC amplitude increased across repetitions, causing the lexicality effect to disappear, with the left inferior frontal, left superior temporal and right superior frontal gyri identified as the most likely neural sources. The lack of repetition effect on FN400 suggests that this component is unrelated to familiarity processes and is only influenced by semantic differences between stimuli. The LPC observations, however, reflect the construction and strengthening of visual memory traces for repeated pseudowords, facilitating their processing over the course of the task.

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