Neural Underpinnings of Age Categorization of Faces in Young Adults

The present study investigated neurocognitive underpinnings of age categorization of faces by integrating behavioral and neuroimaging measures in young adults. Experiment 1 (N = 38) showed faster behavioral responses to older than younger faces in an explicit age categorization task, providing behavioral evidence for earlier age categorization of older than younger faces. Experiments 2 and 3 (N = 38) examined repetition suppression (RS) of electroencephalography signals to younger and older faces which were presented separately in different blocks of trials or alternately in the same block of trials. The results showed RS of the P2 amplitudes (160-200 ms) to older faces but RS of the N2 amplitudes (220-260 ms) to younger faces, suggesting earlier neural encoding of within-category similarity of older (vs. younger) faces. Experiment 4 (N = 28) found RS of magnetoencephalography signals to older faces in the left parahippocampal gyrus, fusiform, posterior superior temporal sulcus, right cuneus, posterior cingulate gyrus, anterior insula, and bilateral anterior temporal lobes at 100-200 ms, and in the right posterior superior temporal sulcus, temporoparietal junction, and bilateral anterior temporal lobes at 350-400 ms. By contrast, RS of magnetoencephalography signals to younger faces occurred in the left anterior insula, right intraparietal sulcus, posterior superior temporal sulcus, and temporoparietal junction at 200-300 ms, suggesting distinct neural networks underlying encoding of within-category similarity of younger and older faces. Together, our behavioral and neuroimaging findings established distinct spatial-temporal profiles of neurocognitive underpinnings of age categorization of younger and older faces and extend our understanding of social categorization of faces in general.