Effective Connectivity in Response to Posture Changes in Elderly Subjects as Assessed Using Functional Near-Infrared Spectroscopy.

Congcong Huo,Gongcheng Xu,Zengyong Li,Ming Zhang,Ying Liu,Lingguo Bu,Lingling Sun

doi:10.3389/fnhum.2018.00098

Abstract

This study aims to assess the posture-related changes in frequency-specific effective connectivity (EC) in elderly subjects by coupling function measured using functional near-infrared spectroscopy (fNIRS). The fNIRS signals were continuously recorded from the bilateral prefrontal cortex (PFC), motor cortex (MC), and occipital lobe (OL) in 17 healthy elderly and 19 healthy young subjects during sitting and standing states. EC was calculated based on Dynamic Bayesian inference in one low frequency interval I: 0.052–0.145 Hz and one very low frequency interval II: 0.021–0.052 Hz. Results show that in response to posture change, the coupling strength significantly increased in interval I of the young group from right PFC to MC (p < 0.05). Meanwhile, the coupling strength of the elderly group was significantly increased in interval II from the left PFC to right PFC (p = 0.008) and to left MC (p = 0.031) in the standing state as compared with that in the sitting state. Compared with that of the young group, the coupling strength of the elderly group was significantly decreased (p < 0.05) between the right PFC and left PFC in interval I and from PFC and OL to MC in interval II during the sitting state. The decreased EC in interval I was also positively correlated with cognitive scores in the elderly group. In addition, the coupling strength from MC to PFC in interval II during standing state was significantly increased in elderly subjects as compared with that in the young group. These results revealed the age-related changes in reorganization of interregional interactions for different postures. These findings may provide evidence of impaired cognitive function in the elderly and can deepen the understanding on age-related changes in neurovascular coupling.

Highlights

Normal aging is related with decreased cognitive functions, including lack of attention, memory loss, and executive function decline (Hedden and Gabrieli, 2004; Kiyoka et al, 2013), which seriously affect their quality of life (Mitchell et al, 2010)
Aging (Vandenbossche et al, 2011; Beurskens et al, 2014). By combining this finding and the main coupling direction (mCD) results across the brain network (Figure 5), we observed that the significantly increased causal interactions from motor cortex (MC) to prefrontal cortex (PFC) in the elderly are a feedback effect
We revealed posture-related changes in frequencyspecific effective connectivity (EC) in elderly subjects based on dynamic Bayesian inference

Summary

Introduction

Normal aging is related with decreased cognitive functions, including lack of attention, memory loss, and executive function decline (Hedden and Gabrieli, 2004; Kiyoka et al, 2013), which seriously affect their quality of life (Mitchell et al, 2010). Regional cerebral blood flow (rCBF) must be allocated appropriately according to compartmentalized brain functions to meet different functional requirements. This process involves neurovascular coupling (Hotta, 2016). From sitting to standing states, the cardiovascular system maintains a stable rCBF to support sufficient levels of brain activity through myogenic, neurogenic, or metabolic mechanisms (Beek et al, 2008). These physiological mechanisms play a role in neurovascular coupling. This study on posture-dependent brain network provides an indepth understanding of the age-related changes in neurovascular coupling

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