Effects of oral deafferentation to chewing-related prefrontal cortex activity

Objectives: Prefrontal cortex (PFC) involves in movement initiation, sensory processing, cognition, memory and learning. Especially concerning chewing-related PFC activity revealed in the previous f-MRI study (Onozuka, 2003), still incompletely understanding was remained in its critical participation for orofacial sensorimotor functions. In this study, we made an attempt to clarify the functional significance of oral sensory input to PFC activity.

Methods: Seven adults (26-55 years old) were subjected in this study. Near-infrared spectroscopy (HITACHI Medical Co, ETG-100) and Bio-amplifiers (NEC Co) were used to detect the hemoglobin concentration ([oxy-Hb]) in PFC and masseter muscle (Mm) EMG activity. Deaffentation of oral sensory input was performed by lidocaine anesthesia into the unilateral inferior alveolar nerve. Chewing task used chewing gum (Lotte Co, Freezone) was composed with 5 times chewing trials and each trial was 10 s duration. Statistical analysis was conducted with paired t-test to compare post-anesthesia condition to pre-anesthesia condition.

Results: Chewing-related PFC activity was indicated in the middle part of dorsal PFC. Chewing performance was modulated by the lidocaine anesthesia, that is chewing cycle duration was significantly (p<0.05) elongated and amplitude of Mm EMG activity was significantly (p<0.05) decreased in post-anesthesia condition (1038.3±382.4 ms, 0.421±0.365 mV, respectively) by comparison with pre-anesthesia condition (703.1±146.8 ms, 0.621±0.38 mV, respectively). Activity of middle part of dorsal PFC in the right hemisphere was significantly (p<0.05) decreased in post-anesthesia condition (0.010±0.014 mMmm) by comparison with pre-anesthesia condition (0.053±0.012 mMmm).

Conclusion: Right middle part of dorsal PFC may dominantly involve in sensory processing and/or sensorimotor integration for the chewing performance.