Regional brain activity during face and word discrimination: simultaneous recording of event-related potentials and positron emission tomography

In order to clarify the brain mechanisms involved in the recognition of fac es. words, and figures, spatiotemporal analyses were carried out with event -related potentials (ERPs) and positron emission tomography (PET) in normal subjects. In the first experiment, we analyzed the ERPs of eight normal su bjects under a passive habituation paradigm using pictures of faces and let ters. In the second experiment, regional cerebral blood flow (rCBF) measure d using PET was obtained simultaneously with the ERP recordings during a co ntinuous performance task (CPT) in 12 normal subjects. This required the ac tive discrimination of famous people's faces, meaningful words consisting o f two Japanese hiragana characters, and simple geometric figures. There wer e similar deflections in the global field power (GFP) in the first 200 ms o f the passive and active tasks, regardless of type of stimuli. This suggest s a common time course in the visual information processing mechanisms duri ng the preattentive stage. Mesiotemporal activity, dominant on the right, w as seen during the face discrimination task in both the PET results and the ERP topographies. In the word task, activity that was clearly dominant on the left was observed at around a 160 ms latency in the posteriotemporal re gion of the ERP topography and this again coincided well with the PET data. The spatiotemporal resolution of the analyses was-improved by combining PE T and topographic ERP studies, and this provided additional neurophysiologi cal information concerning cognitive processing.