Löwel S, Singer W
Max-Planck-Institut für Hirnforschung, Frankfurt a.M., Germany.
Eur J Neurosci. 1993 Jul 1;5(7):857-69. doi: 10.1111/j.1460-9568.1993.tb00938.x.
In the course of experiments studying the organization of ocular dominance columns in the visual cortex of cats, we noticed that--contrary to common belief--labelling with 2-deoxyglucose after monocular stimulation failed to induce a pattern of ocular dominance columns but resulted in a rather homogenous 2-deoxyglucose uptake throughout area 17 in anaesthetized and paralysed animals. We wondered whether 2-deoxyglucose columns could be obtained in awake animals and/or in strabismic animals, which have a more pronounced segregation of ocular dominance columns. To this end, we investigated 2-deoxyglucose patterns after monocular stimulation in three groups of animals: (i) in awake normally reared cats, (ii) in awake strabismic cats and (iii) in anaesthetized and paralysed strabismic cats. Additionally, we labelled ocular dominance columns with intraocular [3H]proline injections. In all cats, monocular stimulation induced 2-deoxyglucose patterns that were in precise register with the proline-labelled ocular dominance columns in layer IV. Regions of increased 2-deoxyglucose uptake extended in a columnar fashion through all cortical layers. In contrast to normally reared animals, in strabismic cats, the expression of 2-deoxyglucose labelled ocular dominance columns was not abolished by anaesthesia or paralysis. However, there was a difference between the 2-deoxyglucose patterns in the awake normally reared cats and the strabismic animals. In the former, the patches of 2-deoxyglucose labelling were smaller and occupied less territory than the afferents of the stimulated eye in layer IV. Together with the results of the previous study, these data indicate that in awake normally reared and in awake and anaesthetized strabismic cats, but not in anaesthetized and paralysed normally reared animals, monocular stimulation activates selectively neurons in columns that are in register with the termination sites of afferents from the stimulated eye. This suggests the existence of a mechanism in normally reared animals which restricts cortical activation after monocular stimulation to territories that are in register with the afferents from the stimulated eye. This mechanism appears to be effective only when the animals are awake and actively exploring their environment. This and the fact that the active columns were narrower than the terminal fields of the stimulated eye suggest an active inhibitory process, perhaps related to mechanisms of selective attention. The observation that ocular dominance columns persist in strabismic cats even under anaesthesia can be accounted for by the lack of binocular convergence in these animals.
在研究猫视觉皮层中眼优势柱组织的实验过程中，我们注意到——与普遍看法相反——在单眼刺激后用2-脱氧葡萄糖标记未能诱导出眼优势柱的模式，而是在麻醉和瘫痪的动物的17区导致了相当均匀的2-脱氧葡萄糖摄取。我们想知道在清醒动物和/或斜视动物中是否能获得2-脱氧葡萄糖柱，因为斜视动物的眼优势柱分离更为明显。为此，我们在三组动物中研究了单眼刺激后的2-脱氧葡萄糖模式：（i）清醒的正常饲养的猫，（ii）清醒的斜视猫，（iii）麻醉和瘫痪的斜视猫。此外，我们通过眼内注射[3H]脯氨酸标记眼优势柱。在所有的猫中，单眼刺激诱导出的2-脱氧葡萄糖模式与IV层中脯氨酸标记的眼优势柱精确对齐。2-脱氧葡萄糖摄取增加的区域以柱状方式延伸穿过所有皮层。与正常饲养的动物不同，在斜视猫中，麻醉或瘫痪并没有消除2-脱氧葡萄糖标记的眼优势柱的表达。然而，清醒的正常饲养的猫和斜视动物的2-脱氧葡萄糖模式存在差异。在前者中，2-脱氧葡萄糖标记的斑块比IV层中受刺激眼的传入纤维更小，占据的区域更少。结合之前的研究结果，这些数据表明，在清醒的正常饲养的猫以及清醒和麻醉的斜视猫中，但在麻醉和瘫痪的正常饲养的动物中并非如此，单眼刺激选择性地激活了与受刺激眼传入纤维终止位点对齐的柱中的神经元。这表明在正常饲养的动物中存在一种机制，该机制将单眼刺激后的皮层激活限制在与受刺激眼传入纤维对齐的区域。这种机制似乎只有在动物清醒并积极探索其环境时才有效。这一点以及活跃柱比受刺激眼的终末场更窄的事实表明存在一种活跃的抑制过程，可能与选择性注意机制有关。即使在麻醉状态下，斜视猫中的眼优势柱仍然存在，这一观察结果可以通过这些动物缺乏双眼汇聚来解释。
