Hayes T L, Lewis D A
Department of Neuroscience, University of Pittsburgh, PA 15213, USA.
Brain Lang. 1995 Jun;49(3):289-308. doi: 10.1006/brln.1995.1035.
The lateralization of motor speech function to the left hemisphere is supported by multiple lines of evidence, but relatively little is known about the anatomical basis of that specialization. In a preliminary study, we recently reported that area 45 of the left hemisphere (Broca's area) contained a subpopulation of magnopyramidal neurons which were significantly larger than any seen in the homotopic region of the right hemisphere (Hayes & Lewis, 1993a). In the present study we examined a larger sample of cases in order to determine how consistently this difference is present in the population, if it is specific to Broca's area or is a general feature of cortical regions mediating lateralized functions, and whether the subpopulation of large magnopyramidal neurons in left area 45 can be distinguished by their chemical phenotype. In Nissl-stained sections from 19 human brains, the mean (+/- SD) cross-sectional area of the largest layer III pyramidal neurons in area 45 was significantly (p < .0001) greater in the left hemisphere (522.1 +/- 128.3 microns2) than in the right (454.1 +/- 121.5 microns2). This interhemispheric difference appeared to be a unique characteristic of the largest neurons, since the mean size of all layer III pyramids in this area was not significantly different in the left (206.2 +/- 93.5 microns2) and right (213.3 +/- 103.9 microns2) hemispheres. In contrast to area 45, there was no interhemispheric difference in the mean cross-sectional area of the largest layer III pyramids in another lateralized region, primary motor cortex. In addition, in area 46, a region of prefrontal association cortex not known to be functionally lateralized, the mean somal size of the largest layer III pyramidal neurons was significantly (p < .001) smaller in the left hemisphere (402.4 +/- 84.9 microns2) than in the right (437.8 +/- 88.3 microns2). Finally, although the large layer III pyramids in area 45 were immunoreactive for nonphosphorylated neurofilament protein in both hemispheres, the mean cross-sectional area of the largest labeled neurons was significantly larger (p < .002) in the left hemisphere (525.2 +/- 149.0 microns2) than in the right (490.3 +/- 154.1 microns2). These findings demonstrate that layer III of Broca's area contains a distinctive subpopulation of neurons that may play an important role in the specific functional architecture of this region.
运动性言语功能向左侧半球的偏侧化有多种证据支持，但对于这种特化的解剖学基础却知之甚少。在一项初步研究中，我们最近报告称，左侧半球的45区（布罗卡区）包含一群大锥体细胞，其显著大于右侧半球同区域所见的任何细胞（海斯和刘易斯，1993a）。在本研究中，我们检查了更多的病例样本，以确定这种差异在人群中出现的一致性程度，它是否特定于布罗卡区，还是介导偏侧化功能的皮质区域的一般特征，以及左侧45区的大锥体细胞亚群是否可以通过其化学表型来区分。在19个人脑的尼氏染色切片中，45区最大的III层锥体神经元的平均（±标准差）横截面积在左侧半球（522.1±128.3平方微米）显著（p<0.0001）大于右侧半球（454.1±121.5平方微米）。这种半球间差异似乎是最大神经元的独特特征，因为该区域所有III层锥体神经元的平均大小在左侧（206.2±93.5平方微米）和右侧（213.3±103.9平方微米）半球之间没有显著差异。与45区不同，另一个偏侧化区域初级运动皮层中最大的III层锥体神经元的平均横截面积没有半球间差异。此外，在46区，一个未知有功能偏侧化的前额叶联合皮层区域，最大的III层锥体神经元的平均胞体大小在左侧半球（402.4±84.9平方微米）显著（p<0.001）小于右侧半球（437.8±88.3平方微米）。最后，尽管45区的大III层锥体神经元在两个半球中对非磷酸化神经丝蛋白均有免疫反应，但最大的标记神经元的平均横截面积在左侧半球（525.2±149.0平方微米）显著（p<0.002）大于右侧半球（490.3±154.1平方微米）。这些发现表明，布罗卡区的III层包含一个独特的神经元亚群，可能在该区域的特定功能结构中起重要作用。
