Not all snakes are alike: Fear- and not disgust-evoking snakes keep attention of primary visual areas - an fMRI study
Abstract
Snakes are evolutionary salient stimuli that have modulated visual, attentional, and emotional processing that results in appropriate behavioral reactions to them. These circuits involve several subcortical areas related to visual processing (superior colliculus and pulvinar of the thalamus) and the amygdala with its interconnections with an array of neocortical areas in the prefrontal cortex (attention and emotional attachment) and several subcortical structures (hypothalamus, brainstem centers regulating autonomic functions).
The amygdala has interconnections with areas that process a conscious as well as unconscious visual information. The aim of this study was to investigate if snake stimuli attached exclusively to the emotion of fear or disgust are also processed differently during a visual and emotional processing.
Using a block fMRI design, we measured responses of 92 participants to pictures of fear-eliciting and disgust-eliciting snakes. Pictures of leaves were used as a control.
Insula and amygdala activation, often reported in studies dealing with strongly affective fearful and disgusting stimuli, was observed only in a few participants that reported exceptionally high fear and/or disgust. However, the results showed a clear difference between the fear-eliciting and disgust-eliciting snake stimuli.
Activation of the visual cortex (including primary visual area) bilaterally was significantly higher (condition: fear > disgust, p<0.001) when watching the fear-eliciting snakes. The occipital fusiform gyrus, lingual gyrus, and inferior occipital gyrus were bilaterally activated only during the fear-eliciting condition.
These results are in agreement with findings that more extensive activation of the visual system facilitates the perceptual processing of survival-relevant stimuli.