An fMRI Study of the Brain Network Involved in Teeth Tapping in Elderly Adults.

T Kobayashi,H Kondo,H Fukami,Y Sahara,E Ishikawa,K Shibata,M Kubota

doi:10.3389/fnagi.2020.00032

T Kobayashi, H Kondo + Show 5 more

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https://doi.org/10.3389/fnagi.2020.00032

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Abstract

Cortical activity during jaw movement has been analyzed using various non-invasive brain imaging methods, but the contribution of orofacial sensory input to voluntary jaw movements remains unclear. In this study, we used functional magnetic resonance imaging (fMRI) to observe brain activities during a simple teeth tapping task in adult dentulous (AD), older dentulous (OD), and older edentulous subjects who wore dentures (OEd) or did not wear dentures (OE) to analyze their functional network connections. (1) To assess the effect of age on natural activation patterns during teeth tapping, a comparison of groups with natural dentition—AD and OD—was undertaken. A general linear model analysis indicated that the major activated site in the AD group was the primary sensory cortex (SI) and motor cortex (MI) (p < 0.05, family wise error corrected). In the OD group, teeth tapping induced brain activity at various foci (p < 0.05, family wise error corrected), including the SI, MI, insula cortex, supplementary motor cortex (SMC)/premotor cortex (PMA), cerebellum, thalamus, and basal ganglia in each group. (2) Group comparisons between the OD and OEd subjects showed decreased activity in the SI, MI, Brodmann’s area 6 (BA6), thalamus (ventral posteromedial nucleus, VPM), basal ganglia, and insular cortex (p ¡ 0.005, uncorrected). This suggested that the decreased S1/M1 activity in the OEd group was related to missing teeth, which led to reduced periodontal afferents. (3) A conjunction analysis in the OD and OEd/OE groups revealed that commonly activated areas were the MI, SI, cerebellum, BA6, thalamus (VPM), and basal ganglia (putamen; p < 0.05, FWE corrected). These areas have been associated with voluntary movements. (4) Psychophysiological interaction analysis (OEd vs OE) showed that subcortical and cortical structures, such as the MI, SI, DLPFC, SMC/PMA, insula cortex, basal ganglia, and cerebellum, likely function as hubs and form an integrated network that participates in the control of teeth tapping. These results suggest that oral sensory inputs are involved in the control of teeth tapping through feedforward control of intended movements, as well as feedback control of ongoing movements.

Highlights

Orofacial muscles are involved in several behaviors, including elemental and semiautomatic movements
Since functional magnetic resonance imaging (fMRI) studies rely on the detection of a weak signal in the presence of substantial noise, many statistical tests may lead to falsepositive results regardless of the analytical approach
Statistical maps of brain regions with significant increases in blood-oxygen-level dependent (BOLD) contrast during a teeth tapping task in the older dentulous (OD) and older edentulous (OE) groups are shown in Figures 3, 4, respectively

Summary

Introduction

Orofacial muscles are involved in several behaviors, including elemental (e.g., tongue protrusion and jaw opening) and semiautomatic (e.g., mastication and swallowing) movements. Direct investigation of the human cerebral cortical areas involved in jaw movements is possible due to the advent of noninvasive visualizing techniques such as fMRI, PET, and MEG. Initial PET-based exploration of the cortical areas related to mastication showed that the sensorimotor areas of the cortex were strongly activated and this was followed by activation of the supplementary motor areas, insulae, striatum, and Cb (Momose et al, 1997). Using fMRI, patterns of brain activation associated with mandibular movements (Ishikawa, 2002) during teeth clenching (Tamura et al, 2002; Byrd et al, 2009; Iida et al, 2010) and chewing (Onozuka et al, 2002; Tamura et al, 2003) have been identified, and there is agreement that an experimental task evoked concurrent activity in multiple brain regions. Neither the interconnections of a network have been identified, nor is it known whether these areas comprise a cohesive functional network

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