Rakic P, Suñer I, Williams R W
Section of Neuroanatomy, Yale University School of Medicine, New Haven, CT 06510.
Proc Natl Acad Sci U S A. 1991 Mar 15;88(6):2083-7. doi: 10.1073/pnas.88.6.2083.
The cerebral cortex is divisible into a number of cytoarchitectonic areas, but developmental mechanisms that regulate their number and size remain unknown. Here we provide evidence that reducing the population of selected thalamic fibers projecting into the primary visual cortex (area 17) of monkeys during midgestation induces the formation of a novel cytoarchitectonic area situated along the border of and embedded within area 17. This region, termed area X, differs cytoarchitectonically from both area 17 and the adjacent secondary visual cortex (area 18). We propose that an aberrant combination of thalamic and cortical connections acting on a portion of prospective area 17 deprived of its normal thalamic input may result in formation of a hybrid cortex. Our results support the protomap hypothesis of cortical parcellation and suggest how during evolution new cytoarchitectonic regions may arise by cell-cell interactions that depend on a unique combination of intrinsic properties of cortical neurons and afferent fibers.
大脑皮层可分为多个细胞构筑区，但调节其数量和大小的发育机制仍然未知。在此我们提供证据表明，在妊娠中期减少投射到猴子初级视皮层（17区）的特定丘脑纤维数量，会诱导在17区边界并嵌入其中形成一个新的细胞构筑区。这个区域称为X区，在细胞构筑上与17区和相邻的次级视皮层（18区）均不同。我们提出，丘脑与皮层连接的异常组合作用于部分预期的17区，使其失去正常的丘脑输入，可能导致形成混合皮层。我们的结果支持皮层分区的原地图假说，并提示在进化过程中，新的细胞构筑区可能如何通过依赖于皮层神经元和传入纤维固有特性独特组合的细胞间相互作用而产生。
