Investigation of the role and cortico-cortical interactions of the right occipital face area

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Faces are a rich source of social information, and face perception research has been one of the most active areas in cognitive neuroscience in recent years. Its importance is correspondingly wide ranging and face processing is a key focus in research into social cognition and autism, brain development, computer security processes, memory, aging and basic visual processing. This research has revealed three brain areas that respond preferentially to faces. These face-selective activations are in the fusiform gyrus, the superior temporal sulcus and the inferior occipital gyrus. Leading models of face processing propose that each area plays a particular role in face processing, with the area in the inferior occipital gyrus, commonly known as the occipital face area (OFA), serving as the first stage of face processing. Yet despite the OFA's key role in these models, it has received far less research attention than the other face-selective areas. We have demonstrated that processing in the right OFA can be disrupted using transcranial magnetic stimulation (TMS), a technique that uses a magnetic field to interfere with processing in a small neural region. This provides a powerful new means to investigate face perception. Not only will it allow us to understand the right OFA better, it will also provide a causal method to examine how different face processing areas interact. We will address two fundamental questions: 1) What is the function of the right OFA and when does it contribute to face processing? The right OFA is the closest face area to early visual areas, so models of face processing have proposed that it is the initial stage of face processing--a gateway to face processing in other areas. This view predicts that TMS to right OFA will disrupt performance on any task requiring the face processing network. Some patient data however are inconsistent with the gateway view while neuroimaging evidence indicates that OFA may be specialized for processing high spatial frequency information from faces. We will compare performance on behavioural tasks in the presence or absence of TMS to right OFA to assess its function. As the first stage of face processing, the OFA is expected to be active soon after stimulus presentation. The temporal resolution of TMS allows us to test this prediction, and our recent findings provide support for it. In two experiments, TMS to right OFA only disrupted face processing when pulses were delivered 60 and 100 milliseconds after the face appeared. We will examine whether this time window disrupts other face processing tasks that are affected by TMS to right OFA. 2) What is the relationship between the right OFA and other face-selective areas? The gateway view of the OFA proposes that it provides input to the other face areas. However despite the ubiquity of this notion, very little evidence speaks to this issue. Using functional magnetic brain imaging (fMRI), we will determine whether TMS to right OFA affects the magnitude of the face-selective responses in the fusiform gyrus and the superior temporal sulcus. We will also examine the effects of right OFA TMS on amygdale activity, because although they are not face-selective, they are important for face processing. A weakening of any of these responses would powerfully demonstrate that right OFA and the affected areas do, in fact, form a network. Unlike fMRI, electrophysiological event related potential (ERPs) provide high temporal resolution. Several ERP components show a stronger response to faces than other visual stimuli. If these face-selective components are modulated by application of TMS to right OFA, it will show that the right OFA provides input to the neural generators producing these components.