A functional neuroimaging investigation of the neural systems sustaining identification of faces and proper names

In this thesis, Position Emission Tomography (PET) was used to investigate how the human brain identifies the faces and proper names of famous people. The first experiment illustrated that identifying known individuals from either their faces or their proper names, activated a widespread neural system in the left hemisphere extending from the anterior temporal to the posterior temporo-parietal regions. To investigate the specificity of these responses for famous people, two further PET studies were performed in which famous faces were compared to other categories of objects (animals, man-made objects, body parts, maps and colours) presented as pictures and famous proper names were compared to names of common objects. Both studies revealed that a specific region in the left anterior temporal lobe was more active for famous faces and proper names than for objects, suggesting a segregation of the neural substrates necessary for retrieving semantic attributes about known people. Alternatively, the preferential response of the anterior temporal cortex for famous people could be explained by greater demands on semantic retrieval processes when the semantic attributes of a stimulus are unique but the visual features are shared by many other members of the same category. To test this hypothesis, the brain response to famous buildings and landmarks was investigated since they are linked, like famous faces, to unique semantic information. Indeed, the anterior temporal lobe was activated by famous buildings as well as famous faces. These studies on normal subjects therefore suggested that the anterior temporal lobe is implicated in retrieval of specific semantic information about unique items. However, in normal language processing, identification and naming occur together highly automatically and it is difficult to disentangle them. A patient with a severe deficit in naming (anomia) famous faces was therefore studied. The patient was able to access semantic but not lexical information and showed a normal anterior temporal cortex response. Taken together, the results of both normal and patient studies suggest that the left anterior temporal cortex is involved in: i) Retrieving specific semantic information about known people regardless of the modality of presentation of the stimuli, i.e. both from faces and proper names; ii) Identification of other categories of unique items, such as famous buildings and landmarks; and iii) Identification more than naming