Interpretation of emotional context is a pivotal aspect of understanding social situations. A critical component of this process is assessment of danger levels in the surrounding, which may have a direct effect on the organism's survival. The limbic system has been implicated in mediating this assessment. In situations of uncertainty, the evaluation process may also call for greater involvement of prefrontal cortex for decision-making and planning of an appropriate behavioral response. In the following study, morphed face images depicting emotional expressions were used to examine brain correlates of subjective uncertainty and perceptual ambiguity regarding danger. Fear and neutral expressions of 20 faces were morphed, and each of the face videos was divided into three sequences of equal length representing three levels of objective certainty regarding the expressions neutral, fear, and ambiguous. Sixteen subjects were scanned in a 1.5-T scanner while viewing 60 × 6-sec video sequences and were asked to report their subjective certainty regarding the level of danger surrounding the face on a four-level scale combining definite/maybe and danger/no-danger values. The individual responses were recorded and used as the basis for a “subjective protocol” versus an “objective protocol.” Significant activations of the amygdala, dorsomedial prefrontal cortex, and dorsolateral prefrontal cortex were observed under the subjective protocol of internally driven uncertainty, but not under objective stimuli-based ambiguity. We suggest that this brain network is involved in generating subjective assessment of social affective cues. This study provides further support to the “relevance detector” theory of the amygdala and implicates its importance to behavior relying heavily on subjective assessment of danger, such as in the security domain context.

Hemispheric lateralization of emotional processing has long been suggested, but its underlying neural mechanisms have not yet been defined. In this functional magnetic resonance imaging study, facial expressions were presented to 10 right-handed healthy adult females in an event-related visual half-field presentation paradigm. Differential activations to fearful versus neutral faces were observed in the amygdala, pulvinar, and superior colliculus only for faces presented in the left hemifield. Interestingly, the left hemifield advantage for fear processing was observed in both hemispheres. These results suggest a leftward bias in subcortical fear processing, consistent with the well-documented leftward bias of danger-associated behaviors in animals. The current finding highlights the importance of hemifield advantage in emotional lateralization, which might reflect the combination of hemispheric dominance and asymmetric interhemispheric information transfer.