Organismal Biology and Anatomy, University of Chicago, Chicago, IL 60637, USA.
J Exp Biol. 2010 Feb 15;213(4):572-84. doi: 10.1242/jeb.036822.
Mammals chew more rhythmically than lepidosaurs. The research presented here evaluated possible reasons for this difference in relation to differences between lepidosaurs and mammals in sensorimotor systems. Variance in the absolute and relative durations of the phases of the gape cycle was calculated from kinematic data from four species of primates and eight species of lepidosaurs. The primates exhibit less variance in the duration of the gape cycle than in the durations of the four phases making up the gape cycle. This suggests that increases in the durations of some gape cycle phases are accompanied by decreases in others. Similar effects are much less pronounced in the lepidosaurs. In addition, the primates show isometric changes in gape cycle phase durations, i.e. the relative durations of the phases of the gape cycle change little with increasing cycle time. In contrast, in the lepidosaurs variance in total gape cycle duration is associated with increases in the proportion of the cycle made up by the slow open phase. We hypothesize that in mammals the central nervous system includes a representation of the optimal chew cycle duration maintained using afferent feedback about the ongoing state of the chew cycle. The differences between lepidosaurs and primates do not lie in the nature of the sensory information collected and its feedback to the feeding system, but rather the processing of that information by the CNS and its use feed-forward for modulating jaw movements and gape cycle phase durations during chewing.
哺乳动物的咀嚼比爬行动物更有节奏。本研究评估了这种差异的可能原因，涉及到感觉运动系统中爬行动物和哺乳动物之间的差异。从四种灵长类动物和八种爬行动物的运动学数据中计算了张口周期各阶段的绝对和相对持续时间的方差。灵长类动物的张口周期持续时间变化小于构成张口周期的四个阶段的持续时间变化。这表明一些张口周期阶段持续时间的增加伴随着其他阶段持续时间的减少。在爬行动物中，类似的影响则不那么明显。此外，灵长类动物的张口周期各阶段持续时间呈等距变化，即张口周期各阶段的相对持续时间随周期时间的增加变化很小。相比之下，在爬行动物中，张口周期总持续时间的方差与缓慢张开阶段在周期中所占比例的增加有关。我们假设，在哺乳动物中，中枢神经系统包含一个最佳咀嚼周期持续时间的表示，该持续时间使用有关咀嚼周期进行状态的传入反馈来维持。爬行动物和灵长类动物之间的差异不在于所收集的感觉信息的性质及其对进食系统的反馈，而在于中枢神经系统对该信息的处理及其用于在前馈中调节咀嚼过程中的下颌运动和张口周期各阶段的持续时间。
