Functional brain networks reveal the existence of cognitive reserve and the interplay between network topology and dynamics

Johann H Martínez,Fernando Maestú,David López-Sanz,Pedro Gil,Mario Chavez,José A Pineda-Pardo,María Eugenia López,Pedro Ariza,Javier M Buldú

doi:10.1038/s41598-018-28747-6

Abstract

We investigated how the organization of functional brain networks was related to cognitive reserve (CR) during a memory task in healthy aging. We obtained the magnetoencephalographic functional networks of 20 elders with a high or low CR level to analyse the differences at network features. We reported a negative correlation between synchronization of the whole network and CR, and observed differences both at the node and at the network level in: the average shortest path and the network outreach. Individuals with high CR required functional networks with lower links to successfully carry out the memory task. These results may indicate that those individuals with low CR level exhibited a dual pattern of compensation and network impairment, since their functioning was more energetically costly to perform the task as the high CR group. Additionally, we evaluated how the dynamical properties of the different brain regions were correlated to the network parameters obtaining that entropy was positively correlated with the strength and clustering coefficient, while complexity behaved conversely. Consequently, highly connected nodes of the functional networks showed a more stochastic and less complex signal. We consider that network approach may be a relevant tool to better understand brain functioning in aging.

Highlights

In recent years, there is an increased interest in studying lifestyle factors that may help to achieve a successful aging
We explored if cognitive reserve (CR) might play a role in both the topology and the dynamics of the functional brain networks in healthy elders while performing a memory task
We classified the participants according to a CR index that combined educational level and occupational attainment into two groups: high or low CR level

Summary

Introduction

There is an increased interest in studying lifestyle factors that may help to achieve a successful aging These factors, such as educational level, leisure activities or intelligence quotient (IQ) have been related to the concept of reserve, which emerges from the absence of a direct relationship between the severity of brain pathology and its clinical manifestations[1]. A previous study from our group[12] observed that healthy elders with a high CR score in comparison with those with low CR score, exhibited less magnetoencephalographic (MEG) functional connectivity during the performance of a memory task These results may suggest that higher CR is related to more effective use of cerebral resources this hypothesis has not been tested yet

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Results

Conclusion