Neural Systems and Behavior, Marine Biological Laboratory, Woods Hole, Massachusetts 02543, USA.
J Neurosci. 2013 Mar 13;33(11):4815-24. doi: 10.1523/JNEUROSCI.4770-12.2013.
Although the neurobiology of rodent facial whiskers has been studied intensively, little is known about sensing in other vibrissae. Here we describe the under-investigated submandibular "whisker trident" on the rat's chin. In this three-whisker array, a unique unpaired midline whisker is laterally flanked by two slightly shorter whiskers. All three whiskers point to the ground and are curved backwards. Unlike other whiskers, the trident is not located on an exposed body part. Trident vibrissae are not whisked and do not touch anything over long stretches of time. However, trident whiskers engage in sustained ground contact during head-down running while the animal is exploring or foraging. In biomechanical experiments, trident whiskers follow caudal ground movement more smoothly than facial whiskers. Remarkably, deflection angles decrease with increasing ground velocity. We identified one putative trident barrel in the left somatosensory cortex and two barrels in the right somatosensory cortex. The elongated putative trident-midline barrel is the longest and largest whisker barrel, suggesting that the midline trident whisker is of great functional significance. Cortical postsynaptic air-puff responses in the trident representation show much less temporal precision than facial whisker responses. Trident whiskers do not provide as much high-resolution information about object contacts as facial whiskers. Instead, our observations suggest an idiothetic function: their biomechanics allow trident whiskers to derive continuous measurements about ego motion from ground contacts. The midline position offers unique advantages in sensing heading direction in a laterally symmetric manner. The changes in trident deflection angle with velocity suggest that trident whiskers might function as a tactile speedometer.
尽管啮齿动物面部触须的神经生物学已经得到了深入研究，但对于其他触须的感知却知之甚少。在这里，我们描述了大鼠下巴上研究较少的下颌“触须三叉戟”。在这个三叉戟排列中，一个独特的不成对中线触须被两个稍短的触须横向包围。所有三根触须都指向地面，并向后弯曲。与其他触须不同，三叉戟不在暴露的身体部位。三叉戟触须不会被刷动，也不会在很长一段时间内接触任何东西。然而，在动物探索或觅食时，三叉戟触须在头朝下奔跑时会持续接触地面。在生物力学实验中，三叉戟触须比面部触须更能平滑地跟随尾部地面运动。值得注意的是，随着地面速度的增加，偏转角度会减小。我们在左侧体感皮层中识别出一个假定的三叉戟桶状结构，在右侧体感皮层中识别出两个桶状结构。细长的假定三叉戟中线桶状结构是最长和最大的触须桶状结构，这表明中线三叉戟触须具有重要的功能意义。三叉戟代表中的皮质突触后空气喷射反应的时间精度远低于面部触须反应。三叉戟触须提供的关于物体接触的高分辨率信息不如面部触须多。相反，我们的观察表明它具有本体感受功能：它们的生物力学允许三叉戟触须从地面接触中获得关于自身运动的连续测量。中线位置提供了以侧向对称方式感知航向的独特优势。三叉戟偏转角度随速度的变化表明，三叉戟触须可能起到触觉速度计的作用。
