Abstract
How do humans discriminate emotion from non-emotion? The specific psychophysical cues and neural responses involved with resolving emotional information in sound are unknown. In this study we used a discrimination psychophysical-fMRI sparse sampling paradigm to locate threshold responses to happy and sad acoustic stimuli. The fine structure and envelope of auditory signals were covaried to vary emotional certainty. We report that emotion identification at threshold in music utilizes fine structure cues. The auditory cortex was activated but did not vary with emotional uncertainty. Amygdala activation was modulated by emotion identification and was absent when emotional stimuli were chance identifiable, especially in the left hemisphere. The right hemisphere amygdala was considerably more deactivated in response to uncertain emotion. The threshold of emotion was signified by a right amygdala deactivation and change of left amygdala greater than right amygdala activation. Functional sex differences were noted during binaural uncertain emotional stimuli presentations, where the right amygdala showed larger activation in females. Negative control (silent stimuli) experiments investigated sparse sampling of silence to ensure modulation effects were inherent to emotional resolvability. No functional modulation of Heschl’s gyrus occurred during silence; however, during rest the amygdala baseline state was asymmetrically lateralized. The evidence indicates changing hemispheric activation and deactivation patterns between the left and right amygdala is a hallmark feature of discriminating emotion from non-emotion in music.
Highlights
Elucidating the threshold of emotional versus non-emotional sound will aide our understanding into the basic properties of emotion
While we currently know very little about the neural basis of sex differences in emotion perception[10], or understand fully the contributions to hemispheric lateralization[10,34,39,40,41,42,43,44,45,53], assessing uncertain emotion at threshold on a range of levels is the key to elucidating the neural components for distinguishing emotional from non-emotional sound
If hemispheric lateralization is a feature in resolving certain from uncertain emotion[10,40,41,44,52,53], or if sex differences in hemispheric lateralization exist[10,53], we would expect the neural response pattern to vary with the psychophysical identification
Summary
Elucidating the threshold of emotional versus non-emotional sound will aide our understanding into the basic properties of emotion. In the auditory cortex, differing contributions of FIS and ENV are utilized to identify emotional content in speech[38] These varying acoustic components within the prosodic contours of pitch[39] are thought to be processed in a right-hemispheric lateralized manner[40,41]. While we currently know very little about the neural basis of sex differences in emotion perception[10], or understand fully the contributions to hemispheric lateralization[10,34,39,40,41,42,43,44,45,53], assessing uncertain emotion at threshold on a range of levels is the key to elucidating the neural components for distinguishing emotional from non-emotional sound. Our overarching aim was to determine the functioning of HG and AMG during the threshold of emotional response (i.e. the minimum emotion necessary to be defined as emotional)
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