Effects of odor on cortical activity during gum chewingOA

Background:Pleasant odors stimulate thalamic neural activity,enhance exercise motivation,and improve motor performance.Previous studies have shown that interactions between chewing and olfaction increase cerebral cortical activity;however,most focused on superficial areas,not deeper brain regions or olfactorymotor integration.This study investigated whether olfactory stimulation enhances cortical activity in motor-related regions(primary motor cortex,supplementary motor area,and dorsolateral prefrontal cortex),primarily in the left hemisphere.--Methods:Thirty-six healthy right-handed individuals aged<35 years participated:Each chewed lemon-flavored(odorized)and odorless gum at a controlled rate(70 chews/min)in a randomized order.After each chewing session,the participants rated the taste,odor,and palatability on a visual analog scale.Changes in cerebral blood flow were monitored using functional near-infrared spectroscopy(fNIRS),focusing on the motor and prefrontal cortices.The masseter muscle and autonomic nervous system activities were also assessed.Data were analyzed using two-way analysis of variance(ANOVA)and paired t-tests with Bonferroni correction.Results:Odorized gum rated higher than odorless gum in the sensory evaluation.Oxy-Hb levels increased during chewing,with odorized gum showing higher levels in the motor control and cognitive regions,particularly the left hemisphere.No differences in masseter activity were observed;however,parasympathetic activity was lower in the odor group,indicating autonomic modulation.Increased motor cortex activation showed no significant somatosensory cortex changes,indicating motor sensory dissociation during odor stimulation.Conclusions:Food odor affects neural activity in the primary motor,supplementary motor,and dorsolateral prefrontal cortices during chewing,enhancing lefthemispheric activity.