Age-Related Difference in Functional Brain Connectivity of Mastication

Abstract

The age-related decline in motor function is associated with changes in intrinsic brain signatures. Here, we investigated the functional connectivity (FC) associated with masticatory performance, a clinical index evaluating general masticatory function. Twenty-six older adults (OA) and 26 younger (YA) healthy adults were recruited and assessed using the masticatory performance index (MPI) and resting-state functional magnetic resonance imaging (rs-fMRI). We analyzed the rs-fMRI FC network related to mastication, which was constructed based on 12 bilateral mastication-related brain regions according to the literature. For the OA and the YA group, we identified the mastication-related hubs, i.e., the nodes for which the degree centrality (DC) was positively correlated with the MPI. For each pair of nodes, we identified the inter-nodal link for which the FC was positively correlated with the MPI. The network analysis revealed that, in the YA group, the FC between the sensorimotor cortex, the thalamus (THA) and the cerebellum was positively correlated with the MPI. Consistently, the cerebellum nodes were defined as the mastication-related hubs. In contrast, in the OA group, we found a sparser connection within the sensorimotor regions and cerebellum and a denser connection across distributed regions, including the FC between the superior parietal lobe (SPL), the anterior insula (aINS) and the dorsal anterior cingulate cortex (dACC). Compared to the YA group, the network of the OA group also comprised more mastication-related hubs, which were spatially distributed outside the sensorimotor regions, including the right SPL, the right aINS, and the bilateral dACC. In general, the findings supported the hypothesis that in OA, higher masticatory performance is associated with a widespread pattern of mastication-related hubs. Such a widespread engagement of multiple brain regions associated with the MPI may reflect an increased demand in sensorimotor integration, attentional control and monitoring for OA to maintain good mastication.

Can you be too old for oral implants? An update on ageing and plasticity in the oro‐facial sensorimotor system

“…This has led to the suggestion that any deficit in sensorimotor function in the elderly may be compensated for by the increased involvement of not only sensorimotor cortex but also other CNS regions (eg, prefrontal cortex) involved in cognitive as well as sensorimotor control . This view is consistent with findings that elderly individuals in contrast to young adults have lower masticatory performance scores and less dense connections between mastication‐related cortical sensorimotor areas and cerebellar areas but have denser connections between the sensorimotor cortex and other cortical areas such as the anterior insular and parietal cortex; they manifest more masticatory‐related areas spatially distributed outside the sensorimotor cortex . While these changes may reflect positive adaptive and compensatory neuroplastic changes, it needs to be kept in mind that some of these areas may themselves be subject to detrimental changes with ageing and so their ability to compensate may be compromised.…”

“…These various CNS regions have been investigated in laboratory animals, and although there are limited details in humans of the underlying CNS mechanisms that regulate and modulate oro‐facial sensorimotor functions, brain‐imaging investigations using functional magnetic resonance imaging (fMRI) in healthy, dentate young to middle‐aged adult human subjects have resulted in findings generally consistent with findings in laboratory animals. The human studies have shown that chewing and tooth clenching or stimulation of oral implants are associated with increased fMRI‐defined activation of brain regions involved in processing sensorimotor information such as the sensorimotor cortex and cerebellum . It has also been shown that there are dense connections between cortical sensorimotor areas and cerebellar regions that are positively correlated with masticatory performance …”

“…The human studies have shown that chewing and tooth clenching or stimulation of oral implants are associated with increased fMRI-defined activation of brain regions involved in processing sensorimotor information such as the sensorimotor cortex and cerebellum. 31,32,[36][37][38][39][40][41][42] It has also been shown that there are dense connections between cortical sensorimotor areas and cerebellar regions that are positively correlated with masticatory performance. 38 Because of the extensive literature bearing on the roles of these many cortical and subcortical regions in sensorimotor control, the following focuses below on just one of these areas as being illustrative of the crucial role played by the CNS in sensorimotor control.…”

“…15,34 This view is consistent with findings that elderly individuals in contrast to young adults have lower masticatory performance scores and less dense connections between mastication-related cortical sensorimotor areas and cerebellar areas but have denser connections between the sensorimotor cortex and other cortical areas such as the anterior insular and parietal cortex; they manifest more masticatory-related areas spatially distributed outside the sensorimotor cortex. 41 While these changes may reflect positive adaptive and compensatory neuroplastic changes, it needs to be kept in mind that some of these areas may themselves be subject to detrimental changes with ageing and so their ability to compensate may be compromised. We should also be mindful that while such widespread masticatory-related brain activity may reflect adaptive neuroplasticity that provides for cognitive as well as sensory and motor adaptive processes to compensate for ageing-related functional declines, they may instead reflect a maladaptive neuroplasticity and an inability to recruit specific CNS areas necessary for efficient performance of oro-facial sensorimotor functions.…”

Jaw sensorimotor control in healthy adults and effects of ageing

“…bilaterally) M1 and S1, and these connections are positively correlated with masticatory efficiency (Fig. ) . However, in edentulous patients (48–72 years old) treated with conventional complete dentures, there is limited activation of these brain regions .…”