RT Journal Article
SR Electronic
T1 Increased prefrontal activity with aging reflects nonspecific neural responses rather than compensation
JF bioRxiv
FD Cold Spring Harbor Laboratory
SP 156935
DO 10.1101/156935
A1 Alexa M. Morcom
A1 Richard N.A. Henson
A1 Cambridge Centre for Ageing and Neuroscience
YR 2017
UL http://biorxiv.org/content/early/2017/06/28/156935.abstract
AB Elevated prefrontal cortex activity is often observed in healthy older adults despite declines in their memory and other cognitive functions. According to one view, this activity reflects a compensatory functional posterior-to-anterior shift, which contributes to maintenance of cognitive performance when posterior cortical function is impaired. Alternatively, the increased prefrontal activity may be less specific, reflecting reduced dedifferentiation or reduced efficiency of neuronal responses due to structural and neurochemical changes accompanying aging. These accounts are difficult to distinguish on the basis of average activity levels within brain regions. Instead, we used a novel model-based multivariate analysis technique, applied to functional magnetic resonance imaging data from an adult-lifespan human sample (N=123; 66 female). Standard analysis replicated the age-related increase in average prefrontal activation during memory encoding, but multivariate tests revealed that this activity did not carry additional information. Indeed, direct tests of the relative contributions of anterior and posterior regions to memory indicated reduced reliance on prefrontal cortex with increasing age. The results contradict the posterior-to-anterior shift hypothesis, suggesting reduced specificity rather than compensation.Significance statement Functional brain imaging studies have often shown increased activity in prefrontal brain regions in older adults. This has been proposed to reflect a compensatory shift to greater reliance on prefrontal cortex, helping to maintain cognitive function. Alternatively, activity may become less specific as people age. This is a key question in the neuroscience of aging. In this study, we used novel tests of how different brain regions contribute to memory for events. We found increased activity in prefrontal cortex in older adults, but this activity carried less information about memory outcomes than activity in visual regions. These findings are relevant for understanding why cognitive abilities decline with age, suggesting that optimal function depends on successful brain maintenance rather than compensation.