Age differences in neural distinctiveness revealed by multi-voxel pattern analysis

Abstract

Current theories of cognitive aging argue that neural representations become less distinctive in old age, a phenomenon known as dedifferentiation. The present study used multi-voxel pattern analysis (MVPA) to measure age differences in the distinctiveness of distributed patterns of neural activation evoked by different categories of visual images. We found that neural activation patterns within the ventral visual cortex were less distinctive among older adults. Further, we report that age differences in neural distinctiveness extend beyond the ventral visual cortex: older adults also showed decreased distinctiveness in early visual cortex, inferior parietal cortex, and medial and lateral prefrontal cortex. Neural distinctiveness scores in early and late visual areas were highly correlated, suggesting shared mechanisms of age-related decline. Finally, we investigated whether older adults can compensate for altered processing in visual cortex by encoding stimulus information across larger numbers of voxels within the visual cortex or in regions outside visual cortex. We found no evidence that older adults can increase the distinctiveness of distributed activation patterns, either within or beyond the visual cortex. Our results have important implications for theories of cognitive aging and highlight the value of MVPA to the study of neural coding in the aging brain.

Figure 1

Region-of-interest analysis of age differences in the distinctiveness of neural activation patterns in ventral visual cortex. Panel A: Older adults showed significantly lower neural distinctiveness than younger adults. Panel B: Older adults showed significantly lower within-category correlations (solid lines) and significantly higher between-category correlations (dotted lines) than younger adults. Error bars denote the standard error of the mean. Asterisks indicate significant effects of age group.

Figure 2

Whole-brain searchlight analysis of age differences in neural distinctiveness. Regions showing significantly higher neural distinctiveness scores for younger compared to older adults are highlighted in red and include bilateral ventral visual cortex (Panel A; z = -6), right striate and left and medial prefrontal cortex (Panel B; z = 8), and bilateral inferior parietal cortex (Panel C; y = -64). No regions showed significantly higher distinctiveness scores for older adults. All coordinates are given in MNI space.

Figure 3

Correlations of neural distinctiveness scores across regions. Correlations between right striate and bilateral ventral visual regions were significant in both younger adults (filled circles; solid lines) and in older adults (open circles; dotted lines). Correlation coefficients are provided in Tables 2 and 3.

Figure 4

Global correlation between neural distinctiveness scores in younger and older adults. Each point describes the neural distinctiveness in the local neighborhood of a single voxel among younger adults (horizontal axis) and older adults (vertical axis). Both groups used the same neural resources to represent visual stimuli (r = .929), but the distinctiveness of any given voxel in older adults was reduced by almost 50% compared to younger adults (β = .519).