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

与咀嚼运动相关的口面部机械感受器放电产生的感觉信息在反射性控制咀嚼运动中起着重要作用。它在检测摄入食物的位置和/或稠度方面也很重要。在本研究中，我们测试了咀嚼对非伤害性口面部感觉传递的影响。为此，在清醒兔咀嚼过程中，记录了面部初级躯体感觉皮质(Face-SI)神经元对低强度电刺激下牙槽神经(Ian)的反应单位活动。整个咀嚼序列分为准备期(PP)、有节奏咀嚼期(RC)和吞咽前期(PS)。共测试了112个面神经元咀嚼的效果。大多数神经元的反应性和JOR在咀嚼的不同时期都有调节。在至少一个咀嚼阶段，Ian诱发的活动在大多数神经元中减弱。相当数量的Face-SI神经元表现出与咀嚼相关的活动，尽管它们对Ian刺激的反应在咀嚼过程中受到强烈抑制(即几乎被“关闭”)。值得注意的是，即使在60%的这类神经元的外周感觉输入被阻断后，咀嚼相关的活动仍然存在。这些结果表明：1)在咀嚼过程中，躯体感觉通路的感觉传递可能受到调节；2)咀嚼过程中面部-SI神经元的活动不一定是运动刺激口面部机械感受器的简单反映，提示食物质地的躯体感觉整合发生在Face-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