Chomiak T, Peters S, Hu B
Department of Clinical Neurosciences and, Hotchkiss Brain Institute, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada.
J Neurophysiol. 2008 Jul;100(1):327-35. doi: 10.1152/jn.90392.2008. Epub 2008 May 7.
Sensory association and parahippocampal cortex in the ventral temporal lobe plays an important role in sensory object recognition and control of top-down attention. Although layer V neurons located in high-order cortical structures project to multiple cortical and subcortical regions, the architecture and functional organization of this large axonal network are poorly understood. Using a large in vitro slice preparation, we examined the functional organization and spike timing properties of the descending layer V axonal network. We found that most, if not all, layer V neurons in this region can form multiple axonal pathways that project to many brain structures, both proximal and remote. The conduction velocities of different axonal pathways are highly diverse and can vary up to more than threefold. Nevertheless for those axonal projections on the ipsilateral side, the speeds of axonal conduction appear to be tuned to their length. As such, spike delivery becomes nearly isochronic along these pathways regardless of projection distance. In contrast, axons projecting to the contralateral hemisphere are significantly slower and do not participate in this lateralized isochronicity. These structural and functional features of layer V network from the ventral temporal lobe may play an important role in top-down control of sensory cue processing and attention.
腹侧颞叶中的感觉联合区和海马旁皮质在感觉物体识别及自上而下的注意力控制中发挥着重要作用。尽管位于高阶皮质结构中的V层神经元投射至多个皮质和皮质下区域，但对这个庞大轴突网络的结构和功能组织却知之甚少。我们利用大型体外脑片标本，研究了下行V层轴突网络的功能组织和峰电位发放时间特性。我们发现，该区域中即便不是全部，也有大多数V层神经元能够形成多条轴突通路，投射至许多近端和远端的脑结构。不同轴突通路的传导速度差异很大，最多可相差三倍以上。然而，对于同侧的那些轴突投射而言，轴突传导速度似乎会根据其长度进行调整。这样一来，无论投射距离如何，沿这些通路的峰电位传递几乎是等时的。相比之下，投射至对侧半球的轴突明显较慢，且不参与这种偏侧化的等时性。腹侧颞叶V层网络的这些结构和功能特征可能在自上而下控制感觉线索处理和注意力方面发挥重要作用。
