Distinct neural systems for the encoding and recognition of topography and faces.

In a series of three positron emission tomography experiments the functional neuroanatomy of four different types of visual stimuli was investigated within the same experimental context. The stimuli were unknown buildings, landscapes, human faces, and animal faces. The purpose of the present study was to compare the stimulus types, both within the same category and across category, by examining if, at encoding (with several seconds exposure to each stimulus) or recognition (over time scales of minutes compared to the seconds of usual perception/one-back studies), common or different neural circuits were activated for all types/categories of stimuli. Within category and although visually very different, the encoding of both buildings and landscapes activated a similar set of brain regions, including bilateral parahippocampal gyrus. This was in contrast to the encoding of both human and animal faces, both of which resulted in activation of the fusiform gyrus bilaterally. Despite the perceptual inputs being identical to those during encoding, the recognition of both buildings and landscapes activated only unilateral right parahippocampal gyrus, while recognition of both human and animal faces activated unilateral right fusiform gyrus. In addition, right superior frontal gyrus and right inferior and medial parietal areas were more active during recognition compared with encoding for all stimulus types. Overall the data identify differential patterns of activation for encoding compared with retrieval of visual stimuli. Furthermore, medial temporal structures specifically are involved in the explicit learning and long-term recognition of topographically relevant stimuli, be they buildings or landscapes, while lateral temporal structures support nontopographical learning and recognition, in this case either human or animal faces.