Abstract

In bimanual coordination, older and younger adults activate a common cerebral network but the elderly also have additional activation in a secondary network of brain areas to master task performance. It remains unclear whether the functional connectivity within these primary and secondary motor networks differs between the old and the young and whether task difficulty modulates connectivity. We applied graph-theoretical network analysis (GTNA) to task-driven fMRI data in 16 elderly and 16 young participants using a bimanual coordination task including in-phase and anti-phase flexion/extension wrist movements. Network nodes for the GTNA comprised task-relevant brain areas as defined by fMRI activation foci. The elderly matched the motor performance of the young but showed an increased functional connectivity in both networks across a wide range of connectivity metrics, i.e., higher mean connectivity degree, connection strength, network density and efficiency, together with shorter mean communication path length between the network nodes and also a lower betweenness centrality. More difficult movements showed an increased connectivity in both groups. The network connectivity of both groups had “small world” character. The present findings indicate (a) that bimanual coordination in the aging brain is associated with a higher functional connectivity even between areas also activated in young adults, independently from task difficulty, and (b) that adequate motor coordination in the context of task-driven bimanual control in older adults may not be solely due to additional neural recruitment but also to aging-related changes of functional relationships between brain regions.

Highlights

  • Aging adversely affects the quality of motor control, and it is commonly accepted that older adults will show poorer motor output with regard to speed, coordination of limb movement, or balance compared to younger adults [1,2,3,4,5,6,7]

  • This study assessed the functional connectivity in the cerebral networks for bimanual coordination in older adults by applying graph-theoretical network analysis

  • The study evaluated functional connectivity aspects in the elderly and is the first to show that bimanual coordination in older adults occurs concomitantly with (a) an increased functional network connectivity between brain areas activated in young adults, and (b) an increased functional connectivity in the overactivation network specific to the older age group

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Summary

Introduction

Aging adversely affects the quality of motor control, and it is commonly accepted that older adults will show poorer motor output with regard to speed, coordination of limb movement, or balance compared to younger adults [1,2,3,4,5,6,7]. It has been shown that older adults commonly recruit a wider network of brain regions than younger adults during task performance [21,24] This increased activation has been reported for a wide range of movement tasks including auditorily paced thumb to index finger tapping [25], finger abduction/adduction [26], wrist flexion/extension [26], sequential finger presses [1,2], hand force production [27,28], hand/foot coordination [17,18,29], and bimanual motor coordination [30]. Whilst Park et al could demonstrate increased network connectivity in parietal-occipital cerebellar related networks during dominant hand use in older subjects, their study focused on efficiency of information transfer as sole measure but provided no information on other aspects of functional connectivity associated with aging

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