Are There Sex Differences in Brain Activity in Response to Active Tactile Stimulation?

Tactile information plays a crucial role in object recognition, spatial localization, and motor control. In elucidating the neural basis of these processes, it is critically important to clarify the underlying neural mechanisms of active tactile stimulation. This study aimed to examine brain activation patterns elicited by active tactile stimulation using stress balls of different hardness levels (soft, medium, and hard) with functional magnetic resonance imaging (fMRI) and to investigate their relationship with sex differences and subjective evaluations. Participants were 77 healthy right-handed young adults (37 males and 40 females) who performed a task involving gripping a stress ball at a force of 5 kg once per second under each condition. Following the scanning session, subjective ratings of hardness and comfort were obtained using a nine-point Likert scale. Across all conditions, activation was consistently observed in sensorimotor-related regions such as the postcentral gyrus, precentral gyrus, thalamus, and cerebellum, indicating stable engagement of these areas during active tactile processing. Notably, the medium condition elicited additional activation in higher-order cognitive and emotional regions, including the angular gyrus, posterior cingulate cortex, and hippocampus, suggesting that moderate stimulation may enhance introspective processing and emotional evaluation. Although no statistically significant differences were detected between sexes in the contrast analyses, subjective evaluations showed that, in the medium condition only, males rated the stimulation as significantly more pleasant than females. These findings indicate that active tactile stimulation primarily engages the sensorimotor network, while the strength and perceived comfort of the stimulus can influence emotional and cognitive processing. Furthermore, although clear sex-related differences in neural activity were not observed, perceptual differences between males and females may still occur.