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Exposure of mice to a 24 h light:dark:light:dark (LDLD) cycle with dimly illuminated nights induces the circadian timing system to program two intervals of activity and two intervals of rest per 24 h cycle and subsequently allows entrainment to a variety of extraordinary light regimens including 30 h LDLD cycles. Little is known about critical lighting requirements to induce and maintain this non-standard entrainment pattern, termed "bifurcation," and to enhance the range of apparent entrainment. The current study determined the necessary duration of the photophase for animals to bifurcate and assessed whether requirements for maintenance differed from those for induction. An objective index of bifurcated entrainment varied with length of the photophase over 4-10 h durations, with highest values at 8 h. To assess photic requirements for the maintenance of bifurcation, mice from each group were subsequently exposed to the LDLD cycle with 4 h photophases. While insufficient to induce bifurcation, this photoperiod maintained bifurcation in mice transferred from inductive LDLD cycles. Entrainment to 30 h LDLD cycles also varied with photoperiod duration. These studies characterize non-invasive tools that reveal latent flexibility in the circadian control of rest/activity cycles with important translational potential for addressing needs of human shift-workers.

While previous research has investigated the effects of emotional videos on peripheral physiological measures and conscious experience, this study extends the research to include electrocortical measures, specifically the steady‐state visual‐evoked potential (ssVEP). A carefully curated set of 45 videos, designed to represent a wide range of emotional and neutral content, were presented with a flickering border. The videos featured a continuous single‐shot perspective, natural soundtrack, and excluded elements associated with professional films, to enhance realism. The results demonstrate a consistent reduction in ssVEP amplitude during emotional videos which strongly correlates with the rated emotional intensity of the clips. This suggests that narrative audiovisual stimuli have the potential to track dynamic emotional processing in the cortex, providing new avenues for research in affective neuroscience. The findings highlight the potential of using realistic video stimuli to investigate how the human brain processes emotional events in a paradigm that increases ecological validity. Future studies can further develop this paradigm by expanding the video set, targeting specific cortical networks, and manipulating narrative predictability. Overall, this study establishes a foundation for investigating emotional perception using realistic video stimuli and has the potential to expand our understanding of real‐world emotional processing in the human brain. Affective neuroscience research depends on the ability to evoke states of emotion that are comparable to real‐life situations. Here we demonstrate a novel laboratory paradigm in which electrocortical effects can be estimated during naturalistic emotional multimodal video perception. Realistic video stimuli may enable research questions regarding dynamic emotional processes to be investigated. [ABSTRACT FROM AUTHOR]

The early posterior negativity (EPN) has been shown to be enhanced by emotional relative to neutral scene perception. A subset of studies has also reported a bias in the EPN toward pleasant relative to unpleasant scenes. Functional MRI research has also identified a region in lateral occipital cortex that shows a sensitivity to the visual perception of body parts, which may contribute to the EPN. Here, we assess the roles of rated scene pleasantness and the depiction of body parts on modulation of the EPN in two studies, using scenes that are chosen to be of equivalent perceptual complexity. In Study 1, we presented two distinct highly pleasant and arousing scene contents (erotic couples and moments of jubilant victory) as well as neutral people, threat, and mutilation scenes. As in prior research, the EPN was enhanced by emotionally arousing scenes, with the greatest modulation evoked by erotic scenes, although victory scenes elicited stronger ratings of pleasantness and equivalent ratings of arousal. This result suggests that the EPN may be sensitive to distinct features found in erotic scenes. To determine the extent to which body part perception modulates the EPN, Study 2 compared EPN modulation evoked by erotic scenes with nonerotic nudist scenes. Ratings of pleasantness and arousal were reduced, yet nudist scenes led to stronger modulation of the EPN compared to erotic scenes. These data indicate that, in addition to the emotional intensity of scenes, modulation of the EPN may in part reflect the discrimination of unclothed body parts. The early posterior negativity (EPN) is enhanced by emotionally arousing relative to neutral scene perception. Here, using scene categories balanced for perceptual complexity, we present data from two studies advocating that, in addition to emotional arousal, the depiction of unclothed body parts contributes to the modulation of the EPN. These results suggest that EPN may reflect a combination of emotional and feature‐based effects possibly driven by a heightened sensitivity to human body cues. [ABSTRACT FROM AUTHOR]