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

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.

Resting-state and vocabulary tasks distinctively inform on age-related differences in the functional brain connectome

“…Results did not show the expected interaction between connectivity and accuracy scores in relation with aging, as was originally reported during RS (Andrews-Hanna et al, 2007b;Damoiseaux et al, 2008;Jockwitz et al, 2017;Onoda, Ishihara, & Yamaguchi, 2012). In fact, connectivity studies that used tasks tapping into preserved language abilities in aging (e.g., word production or syntax comprehension task) often similarly failed to find associations between brain function and performance scores (Agarwal et al, 2016;Chan et al, 2017;Davis, Zhuang, Wright, & Tyler, 2014;Diaz, Rizio, & Zhuang, 2016;Hoyau et al, 2018;La et al, 2016;Marsolais, Perlbarg, Benali, & Joanette, 2014;Meunier, Stamatakis, & Tyler, 2014;Tyler et al, 2010). This lack of association suggests that age-related changes tend to fade when task complexity is controlled.…”

“…This observation contradicts our initial hypothesis. Previous work indeed reported increases within the fronto-temporal network (Meinzer, 2012;Agarwal, Stamatakis, Geva, & Warburton, 2016), which are suspected to reflect top-down mechanism in support to cognitive performance (compensation). These two studies used fluency tasks and a phonological rhyming judgment task, respectively, that place more demand on executive and phonological processes than the word semantic tasks used here.…”

The superior longitudinal fasciculus and its functional triple-network mechanisms in brooding

“…Across both samples, microstructural connectivity of the right SLF was also significantly lower in females relative to males, and negatively correlated with age. Hence, SLF asymmetry may be a critical neurodevelopmental biomarker of brooding (Shi et al, 2013; Westlye et al, 2010; Agarwal et al, 2016; Klingberg et al, 1999; Ugwu et al, 2014), albeit future longitudinal dMRI studies will be needed to confirm this. Still, abnormal cerebral lateralization has been hypothesized as far back as Martin's 1989 Goal-Progress Theory of brooding (Martin and Tesser, 1989; Martin et al, 2008) even though this has never been shown using measures of white-matter microstructure specifically.…”

Stuck in a State of Inattention? Functional Hyperconnectivity as an Indicator of Disturbed Intrinsic Brain Dynamics in Adolescents With Concussion: A Pilot Study

“…Hyperconnectivity represents a deviation from the healthy state and is usually interpreted as maladaptive plasticity resulting from the brain injury ( Johnson et al., 2012 ; Newsome et al., 2016 ; Churchill et al., 2017 ), particularly when associated with impaired cognition. Hyperconnectivity has also been observed with preserved or recovered cognitive performance and may represent positive functional plasticity as a compensation for persistent structural alterations ( Shumskaya et al., 2012 ; Bharat et al., 2015 ; Burianová et al., 2015 ; Czerniak et al., 2015 ; Marstaller et al., 2015 ; Olsen et al., 2015 ; Agarwal et al., 2016 ; Harris et al., 2016 ; Iraji et al., 2016 ); however, little is known about the nature of the underlying processes of this pattern or its functional significance.…”