Horton Jonathan C, Adams Daniel L
Beckman Vision Center, 10 Koret Way, University of California, San Francisco, CA 94143-0730, USA.
Philos Trans R Soc Lond B Biol Sci. 2005 Apr 29;360(1456):837-62. doi: 10.1098/rstb.2005.1623.
This year, the field of neuroscience celebrates the 50th anniversary of Mountcastle's discovery of the cortical column. In this review, we summarize half a century of research and come to the disappointing realization that the column may have no function. Originally, it was described as a discrete structure, spanning the layers of the somatosensory cortex, which contains cells responsive to only a single modality, such as deep joint receptors or cutaneous receptors. Subsequently, examples of columns have been uncovered in numerous cortical areas, expanding the original concept to embrace a variety of different structures and principles. A "column" now refers to cells in any vertical cluster that share the same tuning for any given receptive field attribute. In striate cortex, for example, cells with the same eye preference are grouped into ocular dominance columns. Unaccountably, ocular dominance columns are present in some species, but not others. In principle, it should be possible to determine their function by searching for species differences in visual performance that correlate with their presence or absence. Unfortunately, this approach has been to no avail; no visual faculty has emerged that appears to require ocular dominance columns. Moreover, recent evidence has shown that the expression of ocular dominance columns can be highly variable among members of the same species, or even in different portions of the visual cortex in the same individual. These observations deal a fatal blow to the idea that ocular dominance columns serve a purpose. More broadly, the term "column" also denotes the periodic termination of anatomical projections within or between cortical areas. In many instances, periodic projections have a consistent relationship with some architectural feature, such as the cytochrome oxidase patches in V1 or the stripes in V2. These tissue compartments appear to divide cells with different receptive field properties into distinct processing streams. However, it is unclear what advantage, if any, is conveyed by this form of columnar segregation. Although the column is an attractive concept, it has failed as a unifying principle for understanding cortical function. Unravelling the organization of the cerebral cortex will require a painstaking description of the circuits, projections and response properties peculiar to cells in each of its various areas.
今年，神经科学领域迎来了芒卡斯尔发现皮质柱50周年。在这篇综述中，我们总结了半个世纪的研究，却失望地发现皮质柱可能并无功能。最初，它被描述为一种离散结构，贯穿体感皮层各层，其中包含仅对单一感觉模态有反应的细胞，比如深部关节感受器或皮肤感受器。随后，在众多皮质区域都发现了柱的实例，这使得最初的概念得以扩展，涵盖了各种不同的结构和原理。现在，“柱”指的是任何垂直簇中的细胞，它们对任何给定的感受野属性具有相同的调谐。例如，在纹状皮层中，具有相同眼优势的细胞被归为眼优势柱。令人费解的是，眼优势柱在某些物种中存在，而在其他物种中则不存在。原则上，应该可以通过寻找与眼优势柱的存在与否相关的视觉表现的物种差异来确定它们的功能。不幸的是，这种方法毫无成效；尚未发现任何似乎需要眼优势柱的视觉能力。此外，最近的证据表明，眼优势柱的表达在同一物种的个体之间，甚至在同一个体的视觉皮层的不同部分，都可能有很大差异。这些观察结果给眼优势柱具有某种功能的观点以致命一击。更广泛地说，“柱”这个术语还表示解剖投射在皮质区域内或之间的周期性终止。在许多情况下，周期性投射与某些结构特征有着一致的关系，比如V1中的细胞色素氧化酶斑或V2中的条纹。这些组织区室似乎将具有不同感受野特性的细胞分隔到不同的处理流中。然而，尚不清楚这种柱状隔离形式能带来什么优势（如果有的话）。尽管柱是一个很有吸引力的概念，但它作为理解皮质功能的统一原则却失败了。要弄清楚大脑皮层的组织，需要对其各个区域中细胞特有的回路、投射和反应特性进行细致的描述。
