Dominant hemisphere functional networks compensate for structural connectivity loss to preserve phonological retrieval with aging.

Smriti Agarwal,Elizabeth A Warburton,Emmanuel A Stamatakis,Sharon Geva

doi:10.1002/brb3.495

Smriti Agarwal, Elizabeth A Warburton + Show 2 more

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https://doi.org/10.1002/brb3.495

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Abstract

IntroductionLoss of hemispheric asymmetry during cognitive tasks has been previously demonstrated in the literature. In the context of language, increased right hemisphere activation is observed with aging. Whether this relates to compensation to preserve cognitive function or dedifferentiation implying loss of hemispheric specificity without functional consequence, remains unclear.MethodsWith a multifaceted approach, integrating structural and functional imaging data during a word retrieval task, in a group of younger and older adults with equivalent cognitive performance, we aimed to establish whether interactions between hemispheres or reorganization of dominant hemisphere networks preserve function. We examined functional and structural connectivity on data from our previously published functional activation study. Functional connectivity was measured using psychophysiological interactions analysis from the left inferior frontal gyrus (LIFG) and the left insula (LINS), based on published literature, and the right inferior frontal gyrus (RIFG) based on our previous study.ResultsAlthough RIFG showed increased activation, its connectivity decreased with age. Meanwhile, LIFG and LINS connected more bilaterally in the older adults. White matter integrity, measured by fractional anisotropy (FA) from diffusion tensor imaging, decreased significantly in the older group. Importantly, LINS functional connectivity to LIFG correlated inversely with FA.ConclusionsWe demonstrate that left hemispheric language areas show higher functional connectivity in older adults with intact behavioral performance, and thus, may have a role in preserving function. The inverse correlation of functional and structural connectivity with age is in keeping with emerging literature and merits further investigation with tractography studies and in other cognitive domains.

Highlights

Loss of hemispheric asymmetry during cognitive tasks has been previously demonstrated in the literature
While the connectivity changes in the younger group may not necessarily have been performance related, our aim was to assess whether any differences in functional connectivity between the older and younger groups contribute to preservation of performance, as well as, examining the role of hemispheric networks involved in phonological retrieval in either group
We further explored the relationship between white matter changes using Diffusion Tensor Imaging (DTI) and changes in network configuration measured by PPI

Summary

Introduction

Loss of hemispheric asymmetry during cognitive tasks has been previously demonstrated in the literature. In the context of language, increased right hemisphere activation is observed with aging Whether this relates to compensation to preserve cognitive function or dedifferentiation implying loss of hemispheric specificity without functional consequence, remains unclear. The HAROLD (Hemispheric Asymmetry Reduction in Older adults) model (Cabeza 2002) suggests that functional brain activity becomes less asymmetrical with age. The compensation hypothesis proposes that contralateral recruitment counteracts cognitive decline Another prominent theory of aging and cognition is Salthouse’s (2010) theory of “cognitive slowing” which states that there is a gradual decline of cognitive abilities with increasing age. Slowing of neural responses in the aging brain have been demonstrated previously and in the context of preserved cognitive ability, may be more widespread (Galdo-Alvarez et al 2009), which is in keeping with the basic conception of the HAROLD model.

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