Roberts James A, Robinson Peter A
School of Physics, University of Sydney, New South Wales 2006, Australia.
J Theor Biol. 2008 Jul 7;253(1):189-201. doi: 10.1016/j.jtbi.2008.03.005. Epub 2008 Mar 18.
A successful physiologically based continuum model of the corticothalamic system is applied to determine the relative contributions of axonal and intrinsic cellular delays to the waveforms of absence seizures. The predicted period of the absence seizure depends linearly on model parameters describing thalamocortical, corticothalamic, intracortical, and synaptodendritic delays, and these dependences are linked to the seizure mechanism by showing how time intervals between peaks in the waveforms depend on the parameters. Counterintuitively, it is found that a peak in the local field potential recorded in the thalamic relay nuclei can precede the peak in the cortical field that drove it, without violating causality, but rendering naive interpretation of time intervals between peaks invalid. We argue that a thalamocortical loop mechanism for absence seizures is consistent with intrathalamic cellular properties being the leading determinant of the frequency of spike-wave discharges in rat genetic models, with the combination of network and cellular properties providing a natural explanation for the lower frequency of human absence seizures. Finally, our results imply that the seizure frequency is not determined by the fastest thalamocortical and corticothalamic fibers, but rather depends on an effective weighted conduction velocity of all pathways present.
一个成功的基于生理学的皮质丘脑系统连续模型被用于确定轴突延迟和内在细胞延迟对失神发作波形的相对贡献。预测的失神发作周期线性依赖于描述丘脑皮质、皮质丘脑、皮质内和突触树突延迟的模型参数，并且通过展示波形峰值之间的时间间隔如何依赖于这些参数，这些依赖性与发作机制相关联。与直觉相反的是，发现在丘脑中继核中记录的局部场电位的峰值可以先于驱动它的皮质场电位的峰值出现，这并不违反因果关系，但使得对峰值之间时间间隔的简单解释无效。我们认为，失神发作的丘脑皮质环路机制与丘脑内细胞特性是大鼠遗传模型中棘波放电频率的主要决定因素相一致，网络和细胞特性的结合为人类失神发作频率较低提供了自然的解释。最后，我们的结果表明，发作频率不是由最快的丘脑皮质和皮质丘脑纤维决定的，而是取决于所有存在通路的有效加权传导速度。
