Peters A, Payne B R, Budd J
Department of Anatomy and Neurobiology, Boston University School of Medicine, Massachusetts 02118.
Cereb Cortex. 1994 May-Jun;4(3):215-29. doi: 10.1093/cercor/4.3.215.
Using data that are available in various publications, a quantitative analysis has been made of the geniculocortical input to layer IVC of the macaque striate cortex. The data suggest that only 1.3-1.9% of the excitatory, or asymmetric synapses in layer IVC alpha of striate cortex are provided by the neurons of the magnocellular layers of the LGN. This amounts to only 18-40 of the 1000-2100 asymmetric synapses that the average layer IVC alpha neuron receives. The parvicellular afferents to layer IVC beta, on the other hand, provide 3.7-8.7% of the asymmetric synapses formed by the average layer IVC beta neuron, or 37-191 synapses to each neuron. If it is assumed that the boutons in the geniculocortical axonal plexuses are evenly spread, it can be calculated that the input to an individual layer IVC neuron is provided by some 24 axonal plexuses. This is regardless of whether the neuron lies in layer IVC alpha or in IVC beta. This calculation suggests that a single axonal plexus provides not more than one or two of the excitatory synapses received by an individual layer IVC alpha neuron, and between one and eight excitatory synapses for a layer IVC beta neuron. Consequently, it is unlikely that the response properties of a particular cortical neuron are dominated by its input from a single geniculate neuron. Since the geniculocortical input essentially determines the response properties of neurons in layer IV of macaque striate cortex, it is surprising that this input amounts to such a small number of synapses to an individual neuron, although we obtained a somewhat similar result in our earlier quantitative analysis of the geniculate input to the striate cortex of the cat (Peters and Payne, 1993). But it has to be questioned whether the low values obtained are correct. Interestingly, the geniculocortical input to cortex has been largely neglected in favor of analyses of intracortical circuitry, but in view of the basic importance of this afferent input, it is suggested that more quantitative data about it should be generated, so that a better assessment can be made of its extent.
利用各种出版物中可得的数据，对猕猴纹状皮层IVC层的膝状体皮质输入进行了定量分析。数据表明，纹状皮层IVCα层中只有1.3 - 1.9%的兴奋性或不对称突触是由外侧膝状体大细胞层的神经元提供的。这仅相当于平均IVCα层神经元所接收的1000 - 2100个不对称突触中的18 - 40个。另一方面，IVCβ层的小细胞传入纤维提供了平均IVCβ层神经元形成的不对称突触的3.7 - 8.7%，即每个神经元有37 - 191个突触。如果假设膝状体皮质轴突丛中的终扣是均匀分布的，那么可以计算出，单个IVC层神经元的输入由约24个轴突丛提供。这与该神经元位于IVCα层还是IVCβ层无关。该计算表明，单个轴突丛为单个IVCα层神经元提供的兴奋性突触不超过一两个，为IVCβ层神经元提供的兴奋性突触在一到八个之间。因此，特定皮层神经元的反应特性不太可能由单个膝状体神经元的输入所主导。由于膝状体皮质输入基本上决定了猕猴纹状皮层IV层神经元的反应特性，所以令人惊讶的是，这种输入到单个神经元的突触数量如此之少，尽管我们在早期对猫纹状皮层的膝状体输入进行定量分析时也得到了 somewhat 类似的结果（彼得斯和佩恩，1993年）。但所获得的低值是否正确仍值得质疑。有趣的是，相对于对皮质内回路的分析，膝状体皮质对皮层的输入在很大程度上被忽视了，但鉴于这种传入输入的基本重要性，建议生成更多关于它的定量数据，以便能更好地评估其范围。
