Direct comparison of the neural substrates of recognition memory for wordsand faces

For the purpose of identifying the relatively specific brain regions relate d to word and face recognition memory on the one hand and the regions commo n to both on the other, regional cerebral blood flow associated with differ ent cognitive tasks for recognition memory was examined using [(H2O)-O-15]P ET in healthy volunteers. The tasks consisted of recognizing two types of s timuli (faces and words) in two conditions (novel and familiar), and two ba seline tasks (reading words and gender classification), The statistical ana lyses used to identify the specific regions consisted of three subtractions : novel words minus novel faces, familiar words minus familiar faces, and r eading words minus gender classification. These analyses revealed relative differences in the brain circuitry used for recognizing words and for recog nizing faces within a defined level of familiarity, In order to find the re gions common to both face and word recognition, overlapping areas in four s ubtractions (novel words minus reading words, novel faces minus gender clas sification, familiar words minus reading words, and familiar faces minus ge nder classification) were identified, The results showed that the activatio n sites in word recognition tended to be lateralized to the left hemisphere and distributed as numerous small loci, and particularly included the post erior portion of the left middle and inferior temporal gyri, These regions may be related to lexical retrieval during written word recognition. In con trast, the activated regions for face recognition tended to be lateralized to the right hemisphere and located in a large aggregated area, including t he right lingual and fusiform gyri, These findings suggest that strikingly different neural pathways are engaged during recognition memory for words a nd for faces, in which a critical role in discrimination is played by seman tic cueing and perceptual loading, respectively, In addition, the investiga tion 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.