Activation of human hippocampal formation during memory for faces: a PET study

Using positron emission tomography, we examined cerebral blood flow changes in human subjects whilst engaged in the visual processing of face stimuli. A task requiring anterograde memory of faces was compared with a control task involving simple gender classification--considered an automatic process that did not require any significant memory component. A second task requiring recognition of famous politicians' faces, and therefore involving long-term "semantic" memory, was also contrasted with the control task. To identify brain regions associated with primary visual processing of the face we compared all tasks against a control population scanned with eyes closed. Our results indicate--(1) The involvement of bilateral lingual/fusiform gyri and the right parahippocampal gyrus in addition to striate cortex in primary visual processing of the face; (2) the involvement of the left hippocampal gyrus in both types of memory; (3) a relative decrease in local cerebral blood flow in the inferior parietal lobules in long-term "semantic" memory. In addition, both memory tasks resulted in a suppression of cerebral blood flow in the left superior temporal cortex. We conclude that right hippocampal regions are involved in a largely automatic, primary processing of faces, while left hippocampal regions are additionally involved when explicit memory for faces is required.