Kaas J H
Department of Psychology, Vanderbilt University, Nashville, TN 37240.
Perspect Dev Neurobiol. 1993;1(2):101-7.
There is compelling evidence that the number of cortical areas is variable across species, ranging from the order of 10 to 20 in species with little neocortex to perhaps a hundred or more in humans. The first mammals had few areas, and more fields evolved in several lines of descent. There are several general possibilities for how new cortical areas emerged in evolution, including the gradual differentiation of one area from another, the addition of new cortical tissue that became invaded by axons from other structures to create new fields, and the sudden duplication of existing areas as a result of mutation. A specific version of a "gradual differentiation" theory is presented. New areas might emerge as a result of a process in which classes of inputs to an area first segregate into modular groups of neurons, and then these modules coalesce to ultimately form totally separate populations. All stages allow expected functions to be mediated, and there might be different functional advantages for each stage. Thus, stages may be stable and change is not inevitable. As a result, all stages are represented in the organizations of existing fields of extant mammals.
有确凿证据表明，不同物种的皮质区域数量各不相同，从新皮质较少的物种中的10到20个左右，到人类中可能有一百个或更多。最早的哺乳动物区域较少，在几条进化谱系中演化出了更多区域。在进化过程中，新的皮质区域出现的方式有几种普遍可能性，包括一个区域从另一个区域逐渐分化、新皮质组织的添加（该组织被来自其他结构的轴突侵入从而形成新区域）以及由于突变导致现有区域突然复制。本文提出了一种“逐渐分化”理论的具体版本。新区域可能是由于这样一个过程而出现的：一个区域的输入类别首先分离成模块化的神经元组，然后这些模块合并最终形成完全独立的群体。所有阶段都能介导预期的功能，并且每个阶段可能有不同的功能优势。因此，阶段可能是稳定的，变化并非不可避免。结果，所有阶段都在现存哺乳动物现有区域的组织中有所体现。
