How Aging Shapes Neural Representations of Space: fMRI Evidence for Broader Direction Tuning Functions in Older Adults

Abstract

Human aging is characterized by losses in spatial cognition as well as reductions in distinctiveness of categoryspecific fMRI activation patterns. One mechanism linking theses two phenomena could be that broader neural tuning functions lead to more signal confusions when tuning-based representations of walking direction are read out. To test this idea, we developed a novel method that allowed us to investigate changes in fMRI-measured pattern similarity while participants navigated in different directions in a virtual spatial navigation task. We expected that adjacent directions are represented more similarly within direction sensitive brain areas, reflecting a tuning-function-like signal. Importantly, heightened similarity might lead downstream areas to become more likely to confuse neighboring directions. We therefore analyzed predictions of a decoder trained on these representations, asking (1) whether decoder confusions between two directions increased proportionally to their angular similarity, (2) and how this differs between age groups. Evidence for tuning-function-like signals was found in the retrosplenial complex and primary visual cortex. Significant age differences in tuning width, however, were only found in the primary visual cortex. Our findings introduce a novel approach to measure tuning specificity using fMRI and suggest broader visual direction tuning in older adults might underlie age-related spatial navigation impairments.