Interactions between chewing and brain activity in humans

The involvement of chewing in brain activity in humans has been studied. In our studies using functional magnetic resonance imaging (fMRI) and behavioral techniques, chewing resulted in a bilateral increase in blood oxygenation leveldependent (BOLD) signals in the sensorimotor cortex, supplementary motor area, insula, thalamus, and cerebellum. In addition, in the first three regions, chewing moderately hard gum produced stronger signals than chewing hard gum. However, in the aged group, the BOLD signal increases were smaller in the first three regions and higher in the cerebellum. Only the aged subjects showed significant increases in various association areas to which input activities in the primary sensorimotor cortex, supplementary area, or insula had positive path coefficients. Furthermore, chewing ameliorates the age-related decrease in hippocampal activities during encoding and that in retrieval memory. The findings suggest the involvement of chewing in memory processes