Timecourse and anatomy of recognizing a familiar face

Abstract

When a familiar person comes into view, visual information, in the form of light, must traverse a vast network of brain regions before it reaches the final stage of conscious recognition of the individual. The present study uses a combination of functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI) to map the flow of visual information in face recognition. In the first part of the study, fMRI was used to map waypoints in the brain critical to recognizing familiar faces. The experiment employed a unique design in which visual information was titrated over time to delay recognition. In each trial, subjects were shown a gray scale image of a famous person (e.g. Bill Clinton) initially occluded by an 8 x 8 matrix of tiles. Tiles were then removed at a rate of 2 tiles/second gradually revealing the image over time. Subject's made a behavioral response the moment they recognized the person in the image. Using this paradigm, recognition of the individual in the image was delayed for several seconds after stimulus onset (mean = 14.67 seconds). The results show a clear delineation between cortical regions contributing to the perceptual encoding of the stimuli and high-level recognition processes. Activity in visual areas implicated in face recognition, including the fusiform gryus and lateral occipital complex, began to rise the moment visual information was presented (i.e. stimulus onset) and maintained a sustained response up to the point of recognition. At this moment, a second wave of activity was observed in frontal regions in the anterior cingulate and insular gyri. In the second half of the study, DTI was used assess the axonal connectivity between cortical regions identified in the fMRI experiment. The results of our initial analysis indicate the majority of inputs from the visual cortices come though the anterior cingulate, implicating this region as a potential bridge point between visual information and conscious recognition