Brain Mechanism Of Fearful Face Processing

Fearful face expression is a kind of social information that represents potential threat,as human beings would show a fearful face expression when there is something dangerous on the surrounding environment.On the side of evolutionary,the rapid and effective identification and responding to threatening information is an important skill to survive for ancient human beings.Different individuals showed different sensitivities to fearful faces,which might reflected by the different response time when people saw a fearful face.Although face processing has long been a concern of researchers,the brain mechanism of this fearful face sensitivity is still not well answered.What are the characteristics of human brain that lead to the individual difference of fearful face processing? And which brain regions might be related to this interaction? The rapid development of neural imaging technology in recent years provide us with a new way to explore these question in more depth.Traditional psychologists had used a variety of research paradigms to study the processing of fearful faces,for instance,the visual search paradigm,which was used in the attention-related studies in early years.The visual search paradigm requires the subjects to find specific target stimuli in multiple stimuli and set several different number of the stimuli.As the number of stimuli increases,researchers obtained the slope function of participants’ response time vs.their response accuracy to measure their sensitivity to the target.By comparing the difference between different searching targets,researchers can find out the mechanism how people process different objects.Previous studies usually found human beings processed fearful faces that represent threatening information much faster than other types of faces.In this study,combined with visual search paradigm and multi-model magnetic resonance imaging,we use behavioral experiments,structural magnetic resonance imaging techniques,and blood-oxygen-level-dependent functional magnetic resonance imaging techniques,to explore what is the brain structural basis of the individual difference of fearful face are processing,how the resting state functional connectivity between brain regions influences the individual difference of fearful face processing,and the interactions of different part of brain regions influence the fearful face processing of people when they performed the fearful face match experiment.The first experiment in our study used fearful face visual search paradigm,we asked the participants to perform an off-line behavioral experiment and structural and resting-state functional MRI scan.The target stimulus of the behavioral experiment includes fearful and neutral face,and there were three settings of stimuli,2,4,and 8 face stimulation.The subjects needed to determine whether there was a target face in the face stimulus and respond as quickly as possible.Among them,no matter what the target was,the distractor stimuli were neutral faces,while the gender of the distractor stimuli was different when the target is neutral face.So we can compare the fearful face sensitivity of the subjects in the same stimulus background.The results showed that the subjects detected the fearful face much faster than neutral face and the search slope of fearful face was much shallower than that of neutral face.The difference of the fearful face search slope and neutral face search slope was calculated as the fearful face sensitivity of each subject.The structural MRI image of each participant was analyzed combined with the fearful face sensitivity index using voxel-based morphometry analysis,and we found a cluster in the left fusiform gyrus was correlated with this index.Then we used this cluster as a region of interest to calculate the resting-state functional connectivity across the whole brain.The results showed that the resting-state functional connectivity between left fusiform gyrus and left ventro-medial prefrontal cortex and right inferior parietal lobe was correlated with the individual difference of fearful face sensitivity.These results indicated that left fusiform gyrus might play a central role in fearful face processing and,and ventro-medial prefrontal cortex and inferior parietal lobe could mediate its function in fearful face processing.The second study used a typical fearful face match task with functional MRI scanning,the subjects were asked to perform the task in the MRI scanner,so we can record their brain activity.We found that when the subjects performed fearful face match task,bilateral fusiform gyrus and brain regions in limbic system showed strong activity.We also used psychophysiological interaction analysis,and found bilateral fusiform gyrus interacted with limbic system and right fusiform gyrus showed connectivity with more brain regions.These results indicated that both the left and right fusiform gyrus play a central role in fearful face processing,but they might be different in specific processing stream.The left fusiform gyrus might mainly process partial characteristics of fearful faces while the right fusiform gyrus was more likely to process the whole fearful face.