Furuta Takahiro, Nakamura Kouichi, Deschenes Martin
Centre de Recherche Université Laval Robert-Giffard, Québec G1J 2G3, Canada.
J Neurosci. 2006 Oct 11;26(41):10548-57. doi: 10.1523/JNEUROSCI.1746-06.2006.
One of the most salient features of primary vibrissal afferents is their sensitivity to the direction in which the vibrissae move. Directional sensitivity is also well conserved in brainstem, thalamic, and cortical neurons of the lemniscal pathway, indicating that this property plays a key role in the organization of the vibrissal system. Here, we show that directional tuning is also a fundamental feature of second-order interpolaris neurons that give rise to the paralemniscal pathway. Quantitative assessment of responses to vibrissa deflection revealed an anisotropic organization of receptive fields with regard to topography, response magnitude, and the degree of angular tuning. Responses evoked by all vibrissae within the receptive field of each cell exhibited a high consistency of direction preference, but a striking difference in angular tuning preference was found among cells that reside in the rostral and caudal divisions of the interpolaris nucleus. Although in caudal interpolaris vectors of angular preference pointed in all directions, in rostral interpolaris virtually all vectors pointed upward, revealing a strong preference for this direction. Control experiments showed that the upward bias did not rely on a preferential innervation of rostral cells by upwardly tuned primary vibrissa afferents, nor did it rely on a direction-selective recruitment of feedforward inhibition. We thus propose that the upward preference bias of rostral cells, which project to the posterior group of the thalamus, emerges from use-dependent synaptic processes that relate to the kinematics of whisking.
初级触须传入神经最显著的特征之一是它们对触须运动方向的敏感性。在脑干、丘脑和lemniscal通路的皮质神经元中，方向敏感性也得到了很好的保留，这表明该特性在触须系统的组织中起着关键作用。在这里，我们表明方向调谐也是产生旁lemniscal通路的二阶中间极神经元的基本特征。对触须偏转反应的定量评估揭示了感受野在地形、反应幅度和角度调谐程度方面的各向异性组织。每个细胞感受野内所有触须诱发的反应在方向偏好上表现出高度一致性，但在中间极核头端和尾端区域的细胞之间发现了角度调谐偏好的显著差异。虽然在尾端中间极，角度偏好向量指向所有方向，但在头端中间极，几乎所有向量都向上，显示出对该方向的强烈偏好。对照实验表明，向上偏向并不依赖于向上调谐的初级触须传入神经对头端细胞的优先支配，也不依赖于前馈抑制的方向选择性募集。因此，我们提出，投射到丘脑后组的头端细胞的向上偏好偏向源于与拂动运动学相关的依赖于使用的突触过程。
