FMRI activity during associative encoding is correlated with cardiorespiratory fitness and source memory performance in older adults

Publication date: Available online 12 January 2017
Source:Cortex
Author(s): Scott M. Hayes, Jasmeet P. Hayes, Victoria J. Williams, Huiting Liu, Mieke Verfaellie
Older adults, relative to younger adults, exhibit age-related alterations in fMRI activity during associative encoding, which contributes to deficits in source memory. Yet, there are remarkable individual differences in brain health and memory performance among older adults. Cardiorespiratory fitness (CRF) is one individual difference factor that may attenuate brain aging, and thereby contribute to enhanced source memory in older adults. To examine this possibility, 26 older and 31 young adults completed a treadmill-based exercise test to evaluate CRF (peak VO2) and functional Magnetic Resonance Imaging (fMRI) to examine brain activation during a face-name associative encoding task. Our results indicated that in older adults, peak VO2 was positively associated with fMRI activity during associative encoding in multiple regions including bilateral prefrontal cortex, medial frontal cortex, bilateral thalamus and left hippocampus. Next, a conjunction analysis was conducted to assess whether CRF influenced age-related differences in fMRI activation. We classified older adults as high or low CRF and compared their activation to young adults. High CRF older adults showed fMRI activation more similar to young adults than low CRF older adults (i.e., reduced age-related differences) in multiple regions including thalamus, posterior and prefrontal cortex. Conversely, in other regions, primarily in prefrontal cortex, high CRF older adults, but not low CRF older adults, demonstrated greater activation than young adults (i.e., increased age-related differences). Further, fMRI activity in these brain regions was positively associated with source memory among older adults, with a mediation model demonstrating that associative encoding activation in medial frontal cortex indirectly influenced the relationship between peak VO2 and subsequent source memory performance. These results indicate that CRF may contribute to neuroplasticity among older adults, reducing age-related differences in some brain regions, consistent with the brain maintenance hypothesis, but accentuating age-differences in other regions, consistent with the brain compensation hypothesis.



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