| The purpose of this dissertation project was to assess both the temporal and anatomical neural properties of spatial attention captured by subliminal fearful faces. To evaluate these properties subjects performed a modified, subliminal fearful face, version of the dot-probe task (MacLeod & Mathews, 1988) while event related potential (ERP) or functional magnetic resonance imaging (fMRI) data were collected. Previous research has revealed a unique set of subcortical neural structures associated with the processing of subliminal fearful faces including the superior colliculus, pulvinar, and amygdala (Liddell et al., 2005; Morris, Ohman, & Dolan, 1999; Whalen, Rauch et al., 1998), which is in contrast to a more cortically based system for conscious fear processing (Ohman, 2005). It has been suggested that the subliminal fear network may be involved in an orienting response towards emotionally salient stimuli. However, up until this point, the role that the amygdala plays in modulating subliminal fear-elicited spatial attention was unknown. We found that subliminal fearful faces influenced processing in central-frontal cortical areas as early as 120 ms and were associated with enhanced activity in the left amygdala, right anterior and posterior cingulate cortex, right middle frontal gyrus (rMFG), left dorsolateral prefrontal cortex (lDLPFC), right posterior parietal cortex (rPPC), right primary somatosensory cortex, left insula, left hippocampus, and several areas in the temporal lobes. Subliminal fearful faces direct spatial attention through a network consisting of the left amygdala, left anterior temporal pole, rPPC, lDLPFC, and rMFG. Enhancements in visual attention were associated with increased activity in contralateral visual cortex, which was observed in amplitude enhancements of the face sensitive N170 (170 ms post subliminal face onset). Additionally, the contralateral modulation of visual cortex by subliminal fearful faces appears to enhance the processing of neutral targets occurring at this unique location in visual space. In the case of left visual field subliminal fearful faces congruent targets elicited activity in a distributed face network including the right fusiform gyrus, left superior temporal sulcus, and right lateral occipital area. Based on these results a neuro-anatomical and temporal model for subliminal fearful face elicited enhancements in visuospatial attention is put forth in which subliminal fearful facial expressions are rapidly relayed to the left amygdala and modulate visual cortical activity as early as 170 ms post face onset. |
