Pallas S L, Sur M
Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge 02139.
J Comp Neurol. 1993 Nov 8;337(2):317-33. doi: 10.1002/cne.903370212.
Although the development of corticocortical projections has been well studied, less is known about the role of sensory inputs in the specification of these connections. As part of an ongoing series of studies in our laboratory, we have examined the role of thalamic input modality in the development of corticocortical connections. These studies involve making unilateral lesions and inducing retinal inputs into the auditory thalamus (MGN) during early development in ferrets, thereby conferring visual responsiveness on primary auditory cortex (AI). In this way we can examine the role of input identity in cortical specification in general, and connectivity patterns specifically. A previous paper (Pallas et al. [1990] J. Comp. Neurol. 298:50-68) described the pattern of thalamocortical and corticothalamic connections of auditory cortex in normal and lesioned animals. This study compares the pattern of auditory corticocortical connections in normal and lesioned animals. We injected neuroanatomical tracers into AI and mapped out the distribution of retrogradely labelled cells in the cortex. We report that the cortical inputs to ferret AI resembled those in cats, and that the pattern of ipsi- and contralateral corticocortical connections of ferret AI with visual input was similar to the normal pattern. Auditory cortex with visual input did not make ectopic connections with visual cortex, but maintained its connections with other auditory cortical areas. These results suggest that the overall corticocortical connections of an area are not influenced by the modality or activity pattern of its inputs. In particular, altering the input activity to a cortical area does not seem to promote the formation of entirely new connections, although small changes in the strength of existing connections are possible (Sur et al. [1990] Trends Neurosci. 13:227-233).
尽管皮质-皮质投射的发育已得到充分研究，但关于感觉输入在这些连接的特化过程中的作用，我们了解得还较少。作为我们实验室正在进行的一系列研究的一部分，我们研究了丘脑输入模式在皮质-皮质连接发育中的作用。这些研究包括在雪貂早期发育过程中进行单侧损伤，并将视网膜输入诱导至听觉丘脑（内侧膝状体），从而赋予初级听觉皮层（AI）视觉反应性。通过这种方式，我们可以总体研究输入特性在皮质特化中的作用，特别是连接模式。之前的一篇论文（帕拉斯等人，[1990]《比较神经学杂志》298:50 - 68）描述了正常和损伤动物中听觉皮层的丘脑-皮质和皮质-丘脑连接模式。本研究比较了正常和损伤动物中听觉皮质-皮质连接的模式。我们将神经解剖学示踪剂注入AI，并绘制出皮质中逆行标记细胞的分布。我们报告称，雪貂AI的皮质输入与猫的相似，并且雪貂AI与视觉输入的同侧和对侧皮质-皮质连接模式与正常模式相似。具有视觉输入的听觉皮层没有与视觉皮层形成异位连接，而是维持了与其他听觉皮层区域的连接。这些结果表明，一个区域的整体皮质-皮质连接不受其输入的模式或活动模式的影响。特别是，改变向一个皮质区域的输入活动似乎并不会促进全新连接的形成，尽管现有连接强度可能会有小的变化（苏尔等人，[1990]《神经科学趋势》13:227 - 233）。
