Catania K C, Kaas J H
Neurobiology Unit, Scripps Institution of Oceanography, La Jolla, California, USA.
J Comp Neurol. 1995 Jan 23;351(4):549-67. doi: 10.1002/cne.903510406.
The nose of the star-nosed mole consists of a star-like array of 22 fleshy appendages that radiate from the nostrils and are moved about to explore the environment. The surface of each appendage, or ray, is densely packed with bulbous receptor organs (Eimer's organs) that are highly responsive to tactile stimulation. Here, we report that these rays have corresponding morphological specializations in somatosensory cortex. Using a stain for the metabolic enzyme, cytochrome oxidase (CO), to reveal subdivisions of cortex, we disclosed a complex pattern of CO-dense stripes or bands separated by sharp lines or septa of low CO staining. Multiunit microelectrode recordings of neural activity evoked by light tactile stimuli in somatosensory cortex of anesthetized moles allowed us to mark some of the bands and other CO-dark regions with small electrolytic lesions and later relate recording results to the CO pattern. The results suggest that the primary somatosensory cortex, S1, has an unusual ventrolateral location and orientation with representations of mouth, nose rays, facial vibrissae, forepaw, and trunk in a rostrocaudal sequence. Within this presumptive S1, the 11 rays of the contralateral nose are represented as a rostral-to-caudal cortical pinwheel of 11 stripes. Cortex ventral to the primary set of stripes contains a second rostrocaudal representation of the rays as a mirror image of the first. This second set of stripes may be part of the second somatosensory area, S2. A third pattern of CO stripes appears to merge partially with caudal stripes of the first two patterns, so that a full pattern of 11 stripes is not obvious. This representation may correspond to the ventral somatosensory area, VS, of other mammals. An extensive area of cortex separated from the nose by a large septum was responsive to stimulation of the forelimb. Auditory cortex is unusually caudal in this mole, and the presumptive primary visual area is relatively small. These specializations of somatosensory cortex in star-nosed moles may be more patent examples of the consequences of more general factors in brain development. The observations are consistent with the general rule that the terminations of sensory projections with discorrelated activity segregate.
星鼻鼹的鼻子由22个肉质附属物组成的星状阵列构成，这些附属物从鼻孔放射状伸出并可移动以探索环境。每个附属物（或触须）的表面密布着对触觉刺激高度敏感的球状感受器器官（艾默氏器官）。在此，我们报告这些触须在体感皮层有相应的形态学特化。利用代谢酶细胞色素氧化酶（CO）染色来揭示皮层的分区，我们发现了由低CO染色的清晰线条或间隔分隔的密集CO条纹或带的复杂模式。在麻醉的鼹鼠体感皮层中，对轻触觉刺激诱发的神经活动进行多单元微电极记录，使我们能够用电解小损伤标记一些条纹和其他CO暗区，随后将记录结果与CO模式相关联。结果表明，初级体感皮层S1具有不寻常的腹外侧位置和方向，以从头尾方向的顺序代表嘴、鼻触须、面部触须、前爪和躯干。在这个假定的S1内，对侧鼻子的11条触须表现为11条条纹的从头至尾的皮质风车状排列。初级条纹组下方的皮层包含触须的第二个从头尾方向的表征，是第一个的镜像。这第二组条纹可能是第二体感区S2的一部分。第三种CO条纹模式似乎部分与前两种模式的尾侧条纹融合，因此11条条纹的完整模式并不明显。这种表征可能对应于其他哺乳动物的腹侧体感区VS。一个与鼻子由大间隔分隔的广泛皮层区域对前肢刺激有反应。在这种鼹鼠中，听觉皮层异常靠后，假定的初级视觉区相对较小。星鼻鼹体感皮层的这些特化可能是大脑发育中更一般因素影响的更明显例子。这些观察结果与感觉投射终止活动不相关则分离的一般规则一致。
