Steen Patricia A, Mason Matthew, Pham Lanchi, Lefebvre Yann, Hickmott Peter W
Department of Psychology, University of California, Riverside, California 92521, USA.
J Comp Neurol. 2007 Feb 1;500(4):634-45. doi: 10.1002/cne.21199.
The cortex is a highly organized structure and this organization is integral to cortical function. However, the circuitry underlying cortical organization is only partially understood, thus limiting our understanding of cortical function. Within the somatosensory cortex, organization is manifest as a map of the body surface. At the level of the cortical circuitry the horizontal connections of Layer 2/3 express a physiological bias that reflects discontinuities within the somatosensory map. Both excitation and inhibition are smaller when evoked from across a representational border, as compared to when they are evoked from within the representation. This physiological bias may be due to a bias in either the strength or number of synapses and/or the number of axons that cross this border and the extent of their arborization. In this study we used both an anterograde (Phaseolus vulgaris leucoagglutinin) and a retrograde (cholera toxin B) tracer to examine Layer 2/3 horizontal projections in rat S1. We determined that there is a bias in the amount of horizontal axonal projections that cross the forepaw/lower jaw border as compared to projections remaining within an individual representation. This bias in axonal projection and the correlated bias in excitation and inhibition may underlie the expression of the representational border.
皮质是一种高度有组织的结构，这种组织对于皮质功能至关重要。然而，皮质组织背后的神经回路仅得到部分理解，因此限制了我们对皮质功能的认识。在体感皮质内，组织表现为体表的图谱。在皮质神经回路层面，第2/3层的水平连接表现出一种生理偏向，反映了体感图谱中的不连续性。与在代表区内诱发相比，当从代表区边界两侧诱发时，兴奋和抑制都较小。这种生理偏向可能是由于突触强度或数量、和/或穿过该边界的轴突数量及其分支范围的偏向所致。在本研究中，我们使用了顺行示踪剂（菜豆白细胞凝集素）和逆行示踪剂（霍乱毒素B）来研究大鼠初级体感皮质（S1）中第2/3层的水平投射。我们确定，与留在单个代表区内的投射相比，穿过前爪/下颌边界的水平轴突投射量存在偏向。这种轴突投射的偏向以及兴奋和抑制的相关偏向可能是代表区边界表达的基础。
