The effect of encoding strategy on the neural correlates of memory for faces

Encoding and recognition of unfamiliar faces in young adults were examined using positron emission tomography to determine whether different encoding strategies would lead to encoding/retrieval differences in brain activity. Three types of encoding were compared: a 'deep' task (judging pleasantness/ unpleasantness), a 'shallow' task (judging right,;left orientation), and an intentional learning task in which subjects were instructed to learn the f aces for a subsequent memory test but were not provided with a specific str ategy. Memory for all faces was tested with an old/new recognition test. A modest behavioral effect was obtained, with deeply-encoded faces being reco gnized more accurately than shallowly-encoded or intent ion al ly-learned f aces. Regardless of encoding strategy, encoding activated a primarily ventr al system including bilateral temporal and fusiform regions and left prefro ntal cortices, whereas recognition activated a primarily dorsal set of regi ons including right prefrontal and parietal areas. Within encoding, the typ e of strategy produced different brain activity patterns,,vith deep encodin g being characterized by left amygdala and left anterior cingulate activati on. There was no effect of encoding strategy on brain activity during the r ecognition conditions. Posterior fusiform gyrus activation was related to b etter recognition accuracy in those conditions encouraging perceptual strat egies, whereas activity in left frontal and temporal areas correlated with better performance during the 'deep' condition. Results highlight three imp ortant aspects of face memory: (1) the effect of encoding strategy was seen only at encoding and not at recognition; (2) left inferior prefrontal cort ex was engaged during encoding of faces regardless of strategy; and (3) dif ferential activity in fusiform gyrus was found, suggesting that activity in this area is not only a result of automatic face processing but is modulat ed by controlled processes. (C) 2001 Elsevier Science Ltd. All rights reser ved.