Structural brain feature is associated with changes of masticatory performance in healthy elderly people: Evidence from longitudinal neuroimaging research over two years.

Background: Human neuroimaging studies have revealed the association between brain structure and masticatory function. However, the majority of the studies adopted a cross-sectional design, which hardly reveals the change in masticatory function and brain structure between different timepoints, and the dynamical association between changes in masticatory function and changes in brain structure has not been elucidated.

Objective: With a longitudinal design, we assessed the association between changes in masticatory performance (MP) and regional brain volume.

Methods: Twenty-two elderly participants received assessments of the number of missing teeth and MP (via colour-changeable chewing gum) when they entered the study (i.e. the initial stage, T ), approximately 6 months later (T ), and approximately 1-2 years later (T ). Difficulty of food intake was assessed using a questionnaire. The participants received magnetic resonance imaging (MRI) at T and T . The brain volume of the motor-related area was estimated using FreeSurfer for MRI data. The associations between different stages were analysed using Spearman's rho correlation coefficients.

Results: (1) Individually, a smaller volume of right primary motor cortex at T was associated with increased MP from T to T , suggesting the brain's role in changing oral functions; (2) higher MP at T was associated with an increased volume of the left superior frontal cortex from T to T p, suggesting a potential effect on brain plasticity, and (3) increased difficulty to eat was associated with decrease MP but not brain volume of motor-related area.

Conclusions: The preliminary findings revealed a complicated pattern of structural brain features and masticatory function in elderly people, and either the hypothesis that the brain predisposes masticatory function or the hypothesis that mastication reshapes the brain is oversimplified.