Exercise-Induced Fitness Changes Correlate with Changes in Neural Specificity in Older Adults.

Maike M Kleemeyer,Nils C Bodammer,Sabine Schaefer,Ulman Lindenberger,Lars Brechtel,Thad A Polk

doi:10.3389/fnhum.2017.00123

Abstract

Neural specificity refers to the degree to which neural representations of different stimuli can be distinguished. Evidence suggests that neural specificity, operationally defined as stimulus-related differences in functional magnetic resonance imaging (fMRI) activation patterns, declines with advancing adult age, and that individual differences in neural specificity are associated with individual differences in fluid intelligence. A growing body of literature also suggests that regular physical activity may help preserve cognitive abilities in old age. Based on this literature, we hypothesized that exercise-induced improvements in fitness would be associated with greater neural specificity among older adults. A total of 52 adults aged 59–74 years were randomly assigned to one of two aerobic-fitness training regimens, which differed in intensity. Participants in both groups trained three times a week on stationary bicycles. In the low-intensity (LI) group, the resistance was kept constant at a low level (10 Watts). In the high-intensity (HI) group, the resistance depended on participants’ heart rate and therefore typically increased with increasing fitness. Before and after the 6-month training phase, participants took part in a functional MRI experiment in which they viewed pictures of faces and buildings. We used multivariate pattern analysis (MVPA) to estimate the distinctiveness of neural activation patterns in ventral visual cortex (VVC) evoked by face or building stimuli. Fitness was also assessed before and after training. In line with our hypothesis, training-induced changes in fitness were positively associated with changes in neural specificity. We conclude that physical activity may protect against age-related declines in neural specificity.

Highlights

Pictures of faces, houses, and many other stimulus categories elicit distinguishable patterns of neural response in ventral visual cortex (VVC)
Evidence suggests that neural specificity declines with increasing age (Grady et al, 1994; Park et al, 2004) and reduced neural specificity is associated with lower cognitive performance in a variety of cognitive tasks in older adults (Park et al, 2010)
There were no baseline differences between participants in the two training groups with respect to age, years of education, MMSE, BMI, fitness, hormone replacement therapy, and treated hypertension (see Table 1 for means and standard deviations (SD) or proportion of participants, respectively)

Summary

Introduction

Houses, and many other stimulus categories elicit distinguishable patterns of neural response in ventral visual cortex (VVC). Using functional magnetic resonance imaging (fMRI), Haxby et al (2001) found distinct neural activation patterns in response to eight stimulus categories within ventral temporal cortex. Evidence suggests that neural specificity declines with increasing age (Grady et al, 1994; Park et al, 2004) and reduced neural specificity is associated with lower cognitive performance in a variety of cognitive tasks in older adults (Park et al, 2010). Age-related declines in neurotransmitter function and neuromodulation have been suggested as underlying mechanisms. Neurocomputational models predict that attenuated neuromodulation lowers a cell’s responsivity and leads to less differentiated neural responses to different stimuli (i.e., less distinct neural representations), which in turn would explain age-related deficits across a wide range of cognitive domains (Li and Sikström, 2002)

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Conclusion