Sunday, April 05, 2009

Aging increases fMR-Adaptation to repeated faces and limits discrimination ability

Age-related ventral-visual activity is characterized by reduced selectivity between categories of visual stimuli such as faces and houses that typically elicit highly specialized responses in the fusiform and parahippocampal brain regions respectively of young adults (Park et al., 2004). This study demonstrates that older adults’ less selective neural response (dedifferentiation) to faces is due to a coarser neural representation than that of young adults for individual faces. In this event-related fMRI adaptation study, 20 young and 20 older participants made same-different judgments to serially presented face-pairs that were either identical (repetition of the same face), moderately different (second face was morphed with 40% of prior face), or completely different (faces from two individuals). In the fusiform regions, older adults showed greatest adaptation during the exact-repetition condition and intermediate adaptation during the moderately-different condition relative to the completely-different condition. Young adults showed a similar pattern of adaptation, but with reduced adaptation magnitudes. This suggests that older adults’ fusiform area was not able to represent facial differences at the same level of sensitivity as young adults. Individual subjects’ adaptation magnitudes positively correlated with behavioral face discrimination thresholds for morphed faces (r = .38). Greater age-related adaptation during the exact-repetition condition suggests older adults’ fusiform face region is particularly sensitive to similarity, whereas young adults have a neural response that is more sensitive to facial differences. The data provide strong evidence for an age-related decrease in representational contrast in the fusiform area that is linked to behavioral differences during perceptual discrimination. [pdf]

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