Somatosensory processing of mastication-induced sensory inputs in the cerebral cortex

感觉信息来源于咀嚼运动相关的口面机械感受器放电，在反射性咀嚼运动控制中具有重要作用。它在检测摄入食物的位置和/或一致性方面也很重要。在本研究中，咀嚼对非伤害性口面感觉传递的躯体感觉通路的影响进行了测试。为了实现这一目标，在清醒的家兔咀嚼过程中，记录了低强度电刺激下牙槽神经（IAN）反应的面部初级躯体感觉皮层（Face-SI）神经元的单单位活动。整个咀嚼序列分为预备期（PP）、节律咀嚼期（RC）和咀嚼前期（PS）。共检测了112个面-SI神经元的咀嚼效应。在咀嚼的不同阶段，大多数神经元的反应性和JOR都受到调制。IAN诱发的活动衰减在大多数的神经元在至少一个咀嚼期。相当数量的面SI神经元表现出咀嚼相关的活动，虽然他们的反应IAN刺激强烈抑制（即几乎“门控”）在咀嚼。值得注意的是，咀嚼相关的活动仍然存在，即使在60%的神经元的外周感觉输入的阻断。结果表明：1）咀嚼过程中，躯体感觉通路的感觉传递可能受到调制; 2）咀嚼过程中面-SI神经元的活动可能不一定是运动诱导的口面机械感受器刺激的简单反映，提示食物质地的躯体感觉整合发生在面-SI内

Sensory information, arising from orofacial mechanoreceptor discharge associated with masticatory movements, has an important role in controlling masticatory movements reflexly. It is also important in detecting position and/or consistency of ingested food. In the present study effects of mastication on non-nociceptive orofacial sensory transmission of the somatosensory pathways were tested. To achieve this, single-unit activities of the face primary somatosensory cortex (face-SI) neurons responding to low-intensity electrical stimulation of the inferior alveolar nerve (IAN) were recorded during mastication in awake rabbits. The entire masticatory sequence was divided into the preparatory period (PP), the rhythmic-chewing period (RC) and the preswallow period (PS). A total of 112 face-SI neurons were tested for the effects of mastication. The responsiveness of most neurons and the JOR were modulated during different periods of mastication. The IAN-evoked activity was attenuated in a majority of the neurons during at least one of the masticatory periods. A considerable number of face-SI neurons showed mastication-related activity although their responsiveness to IAN stimulation was strongly suppressed (i.e. almost "gated out") during mastication. It was notable that mastication-related activity still remained even after the blockage of peripheral sensory inputs in 60% of such neurons. The findings indicate that 1)sensory transmissions of the somatosensory pathways may be modulated during mastication, and that 2)activity of face-SI neurons during mastication may not necessarily be a simple reflection of movement-induced stimulation of orofacial mechanoreceptors, and suggest that somatosensory integration of a texture of food occur within face SI