Relationship between Hardness of Food and Brain Blood Flow

Objectives: The purpose of this experiment was to clarify the relationship between the hardness of the food and the amount of brain blood flow during mastication. Methods: Twenty healthy subjects were asked to chew the four types of gumi-jelly with gelatin content of 5%, 6.5%, 8% and 9.5% on their habitual chewing side for 20 seconds. The masseter muscular activity and the temporal brain blood flow were simultaneously measured by EMG and NIRS (near infra-red spectroscopy). The measuring prove of the NIRS was placed, with the distance between the irradiating part and receptive part set at 4 cm, on the scalp over the cortical masticatory area. First the brain blood flow of prior to, during and after chewing gumi-jelly were investigated. Next the cumulative value of the masseter muscular activity and the amount of blood flow were compared among the four types of gumi-jelly. The comparison between foods was done by the multiple comparisons method according to Bonferroni. Results: The temporal brain blood flow increased significantly for all gumi-jelly during chewing and decreased after chewing and returned to the condition prior to chewing. Also both the cumulative values of masseter muscular activity and the amount of brain blood flow were the lowest for the 5% gelatin gumi-jelly and increased in the order of 6.5%, 8%, and 9.5% and significant differences were found between each and every types of gumi-jelly (p<0.05, s.). Conclusions: From these results it was concluded that the masticatory movement increased the brain blood flow and that the hardness of the food affected the increase and decrease in the amount of brain blood flow.