Functional Hemispheric (A)symmetries in the Aged Brain-Relevance for Working Memory.

Madalena Esteves,Ricardo Magalhães,Paulo Marques,Hugo Leite-Almeida,Carlos Portugal-Nunes,Nuno Sousa,Teresa C Castanho,José M Soares,Armando Almeida,Nadine C Santos

doi:10.3389/fnagi.2018.00058

Abstract

Functional hemispheric asymmetries have been described in different cognitive processes, such as decision-making and motivation. Variations in the pattern of left/right activity have been associated with normal brain functioning, and with neuropsychiatric diseases. Such asymmetries in brain activity evolve throughout life and are thought to decrease with aging, but clear associations with cognitive function have never been established. Herein, we assessed functional laterality during a working memory task (N-Back) in a healthy aging cohort (over 50 years old) and associated these asymmetries with performance in the test. Activity of lobule VI of the cerebellar hemisphere and angular gyrus was found to be lateralized to the right hemisphere, while the precentral gyrus presented left > right activation during this task. Interestingly, 1-Back accuracy was positively correlated with left > right superior parietal lobule activation, which was mostly due to the influence of the left hemisphere. In conclusion, although regions were mostly symmetrically activated during the N-Back task, performance in working memory in aged individuals seems to benefit from lateralized involvement of the superior parietal lobule.

Highlights

In the present study we tested the hypothesis that task related blood oxygen level dependent (BOLD) response occurred in a lateralized fashion which could be associated with working memory performance in an older population
We demonstrated that the majority of the activated areas are activated on the left and right hemispheres, some asymmetries could be observed
Superior parietal lobule laterality was positively correlated with 1-Back performance

Summary

Introduction

The human brain presents several marked structural asymmetries such as the Yakovlevian torque (Toga and Thompson, 2003; Hugdahl, 2011) or the asymmetry of the planum temporale (Takao et al, 2011), as well as chemical left/right unbalances in dopaminergic (Glick et al, 1982), noradrenergic (Oke et al, 1978) and opioidergic (Watanabe et al, 2015) systems.It is known since the early observations by Mark Dax and Paul Broca (Broca, 1861; see Roe and Finger, 1996; Manning and Thomas-Antérion, 2011) that the brain distributes its functional load in an asymmetrical fashion. In aged individuals, marked structural asymmetries have been identified (Esteves et al, 2017) and functional studies have systematically reported decreases in lateralization; such has been observed in word encoding/retrieval (Cabeza et al, 1997; Madden et al, 1999; Stebbins et al, 2002), working memory (Reuter-Lorenz et al, 2000), face recognition (Grady et al, 2002), inhibitory control (Nielson et al, 2002), risk-taking (Lee et al, 2008) and error processing (Zhu et al, 2010). Such bilateral activity pattern has been hypothesized to result from a compensatory recruitment (Cabeza, 2002) and, as cognitively efficient older performers recruit additional contralateral networks (Cabeza et al, 2002; Erickson et al, 2007) symmetrical activation could be a correlate of good cognitive aging

Methods

Results

Conclusion