Neural correlates of person recognition

Abstract

Rapidly identifying known individuals is an essential skill in human society. To elucidate the neural basis of this skill, we monitored brain activity while experimental participants demonstrated their ability to recognize people on the basis of viewing their faces. Each participant first memorized the faces of 20 individuals who were not known to the participants in advance. Each face was presented along with a voice simulating the individual speaking their name and a biographical fact. Following this learning procedure, the associated verbal information could be recalled accurately in response to each face. These learned faces were subsequently viewed together with new faces in a memory task. Subjects made a yes-no recognition decision in response to each face while also covertly retrieving the person-specific information associated with each learned face. Brain activity that accompanied this retrieval of person-specific information was contrasted to that when new faces were processed. Functional magnetic resonance imaging in 10 participants showed that several brain regions were activated during blocks of learned faces, including left hippocampus, left middle temporal gyrus, left insula, and bilateral cerebellum. Recordings of event-related brain potentials in 10 other participants tracked the time course of face processing and showed that learned faces engaged neural activity responsible for person recognition 300-600 msec after face onset. Collectively, these results suggest that the visual input of a recently learned face can rapidly trigger retrieval of associated person-specific information through reactivation of distributed cortical networks linked via hippocampal connections.

Figure 1

Example of a block of face presentations and the defining features of each experimental condition. Each block of faces started with a 300-msec task cue, followed by an 1800-msec fixation cross and 10 face trials (300-msec face and 2100-msec fixation cross). Faces were presented briefly to discourage eye movements and to maximize time-locking of relevant cognitive processes. There were 2 runs of 18 blocks (26.1 sec per block, corresponding to 6 whole-brain scans). The gender task was performed in every third block and the memory task in all other blocks, alternating between heavy-retrieval blocks and light-retrieval blocks. In the memory task, subjects made a recognition judgment for each face and were instructed to covertly retrieve the learned biographical information when cued by the associated face.

Figure 2

Brain activations from the heavy-retrieval vs. light-retrieval contrast. Activation maps were generated according to an analysis of signal change using a threshold of t >4.25 (as shown on color scale) with a cluster threshold of 500 mm³ and connectivity radius of 2.5 mm. Activations are shown superimposed on cross-subject average structural MRI scans. Coronal images are labeled according to Y Talairach coordinate, and these slice locations are shown on a sagital image through the left medial temporal region at the level of X = –23. For each cluster, activity was greater for heavy retrieval than for light retrieval.

Figure 3

Brain potentials for learned faces and new faces. Responses are shown for trials during the memory task in which behavioral responses were correct. Recordings were from scalp locations from the International 10-20 System. These electrode locations are shown as filled circles in a schematic representation of a head viewed from above (F7/F8, C3/C4, P3/P4, O1/O2, and T5/T6); other electrode locations in which EEG data were recorded are shown as open circles.

Figure 4

Temporal progression of topographic maps for electrophysiological differences between learned and new faces. Maps were created using a spline interpolation on the basis of mean amplitude measurements from each of 21 electrode locations (shown as open circles on schematic representations of a head viewed from above) over consecutive 100-msec intervals beginning at the times indicated below each map.