Successful episodic memory retrieval of newly learned faces activates a left fronto-parietal network

Abstract

It is easier to recognize a familiar face than a newly learned face. The neural basis of familiar face recognition has been elucidated in functional imaging and lesion studies. Behavioural and neuropsychological data indicate, however, that brain systems involved in episodic retrieval of familiar and newly learned faces are distinct. In our study, 12 subjects viewed 30 novel faces in an encoding session. In the study condition, event-related functional magnetic resonance imaging (fMRI) was used to compare brain activation during correct recognition of the recently learned faces to that observed during correct rejection of unknown control faces. Differences were present in the left inferior parietal (BA 40) and left medial frontal/anterior cingulate (BA 32/9) cortex. These two regions may be part of a pathway in the dorsal visual stream, responsible for a “feeling of familiarity” in contrast to the ventral pathway in the temporal lobes, which is mainly involved in the recognition of personal identity.

Introduction

Face recognition is a basic human ability with a high degree of social relevance. Even newborns are able to specifically distinguish faces from other objects [32] and age-related decrements in face recognition have been reported [1]. The fusiform gyrus, part of the medial temporal cortex, is specialized for face perception [17] and lesions to occipito-temporal brain areas can lead to an impairment in face recognition (prosopagnosia). Fronto-temporal brain damage can cause syndromes such as the capgras delusion where previously familiar faces can be recognized but lack a feeling of familiarity [8], [29]. Behavioural studies indicate that the cognitive processes for recognising familiar faces are distinct from recognising newly learned faces. An example of this is the ability of subjects to recognise familiar persons even from very low quality images, in contrast to their relatively poor ability to recognize newly learned unfamiliar faces [6], [15]. The mechanisms underlying the recognition of unfamiliar faces are of particular interest for forensic reasons (e.g., eye witnessing) and might be useful in developing automatic, computer-based methods of person identification.

Functional imaging studies that have investigated the neural correlates of familiar face recognition have found medial temporal activation, including the hippocampus [23]. The cerebral regions differentially involved in the recognition of newly learned faces, however, remain elusive. Brain imaging can facilitate the formulation of a theoretical model of unfamiliar face recognition [15]. It is only recently that event-related functional magnetic resonance imaging (fMRI) allowed the distinction between cerebral activation during the retrieval of newly learned items and that of distractor faces in a recognition memory task. We used this technique to investigate brain activation during correct recognition of newly learned faces compared to correct identification of distractor faces. We hypothesized that fusiform and medial temporal areas are involved in face processing per se [17]. Event-related potential (ERP) studies of face recognition demonstrated a parietal and a fronto-central activation when previously learned faces were compared with unknown faces [10], [11]. Similarly, left frontal and parietal areas are most consistently exhibiting stronger activity for old vs. new items during verbal recognition memory tasks in functional imaging studies [27]. Based on these findings, we hypothesized that left parietal and medial frontal cortical regions are involved in the recognition of newly learned faces.