Direct comparison of the neural substrates of recognition memory for words and faces.

For the purpose of identifying the relatively specific brain regions related to word and face recognition memory on the one hand and the regions common to both on the other, regional cerebral blood flow associated with different cognitive tasks for recognition memory was examined using [H215O]PET in healthy volunteers. The tasks consisted of recognizing two types of stimuli (faces and words) in two conditions (novel and familiar), and two baseline tasks (reading words and gender classification). The statistical analyses used to identify the specific regions consisted of three subtractions: novel words minus novel faces, familiar words minus familiar faces, and reading words minus gender classification. These analyses revealed relative differences in the brain circuitry used for recognizing words and for recognizing faces within a defined level of familiarity. In order to find the regions common to both face and word recognition, overlapping areas in four subtractions (novel words minus reading words, novel faces minus gender classification, familiar words minus reading words, and familiar faces minus gender classification) were identified. The results showed that the activation sites in word recognition tended to be lateralized to the left hemisphere and distributed as numerous small loci, and particularly included the posterior portion of the left middle and inferior temporal gyri. These regions may be related to lexical retrieval during written word recognition. In contrast, the activated regions for face recognition tended to be lateralized to the right hemisphere and located in a large aggregated area, including the right lingual and fusiform gyri. These findings suggest that strikingly different neural pathways are engaged during recognition memory for words and for faces, in which a critical role in discrimination is played by semantic cueing and perceptual loading, respectively. In addition, the investigation of the regions common to word and face recognition indicates that the anterior and posterior cingulate have dissociable functions in recognition memory that vary with familiarity, and that the cerebellum may serve as the co-ordinator of all four types of recognition memory processes.