Converging electrophysiological and hemodynamic findings indicate sensory processing of emotional pictures is preferred to that of neutral pictures. Whereas neuroimaging studies of emotional picture perception have employed stimulus durations lasting several seconds, recent electrocortical investigations report early visual cortical discrimination between emotionally arousing and neutral picture processing. Here, we use a hybrid picture presentation paradigm covering a range of rapid presentation rates (0.75–6 Hz), while visual system activity is recorded with functional magnetic resonance imaging. Results demonstrate widespread sensitivity to emotional arousal in the secondary and inferior temporal visual cortex. Furthermore, activity in the lateral inferior occipital and medial inferior temporal visual cortex revealed equivalent emotion-sensitive activation across all presentation rates. Results further support the notion that attention and perceptual processing are in part directed by underlying motivational systems.
Abstract Electrophysiological studies of human visual perception typically involve averaging across trials distributed over time during an experimental session. Using an oscillatory presentation, in which affective or neutral pictures were presented for 6 s, flickering on and off at a rate of 10 Hz, the present study examined single trials of steady‐state visual evoked potentials. Moving window averaging and subsequent Fourier analysis at the stimulation frequency yielded spectral amplitude measures of electrocortical activity. Cronbach's alpha reached values >.79, across electrodes. Single‐trial electrocortical activation was significantly related to the size of the skin conductance response recorded during affective picture viewing. These results suggest that individual trials of steady‐state potentials may yield reliable indices of electrocortical activity in visual cortex and that amplitude modulation of these indices varies with emotional engagement.
The ventromedial prefrontal cortex (vmPFC) is a major hub of the reward system and has been shown to activate specifically in response to pleasant / rewarding stimuli. Previous studies demonstrate enhanced pleasant cue reactivity after single applications of transcranial direct current stimulation (tDCS) to the vmPFC. Here we present a pilot case study in which we assess the cumulative impact of multiple consecutive vmPFC-tDCS sessions on the processing of visual emotional stimuli in an event-related MEG recording design. The results point to stable modulation of increased positivity biases (pleasant > unpleasant stimulus signal strength) after excitatory vmPFC stimulation and a reversed pattern (pleasant < unpleasant) after inhibitory stimulation across five consecutive tDCS sessions. Moreover, cumulative effects of these emotional bias modulations were observable for several source-localized spatio-temporal clusters, suggesting an increase in modulatory efficiency by repeated tDCS sessions. This pilot study provides evidence for improvements in the effectiveness and utility of a novel tDCS paradigm in the context of emotional processing.
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