Rucci M, Tononi G, Edelman G M
The Neurosciences Institute, San Diego, California 92121, USA.
J Neurosci. 1997 Jan 1;17(1):334-52. doi: 10.1523/JNEUROSCI.17-01-00334.1997.
In the optic tectum (OT) of the barn owl, visual and auditory maps of space are found in close alignment with each other. Experiments in which such alignment has been disrupted have shown a considerable degree of plasticity in the auditory map. The external nucleus of the inferior colliculus (ICx), an auditory center that projects massively to the tectum, is the main site of plasticity; however, it is unclear by what mechanisms the alignment between the auditory map in the ICx and the visual map in the tectum is established and maintained. In this paper, we propose that such map alignment occurs through a process of value-dependent learning. According to this paradigm, value systems, identifiable with neuromodulatory systems having diffuse projections, respond to innate or acquired salient cues and modulate changes in synaptic efficacy in many brain regions. To test the self-consistency of this proposal, we have developed a computer model of the principal neural structures involved in the process of auditory localization in the barn owl. This is complemented by simulations of aspects of the barn owl phenotype and of the experimental environment. In the model, a value system is activated whenever the owl carries out a foveation toward an auditory stimulus. A term representing the diffuse release of a neuromodulator interacts with local pre- and postsynaptic events to determine synaptic changes in the ICx. Through large-scale simulations, we have replicated a number of experimental observations on the development of spatial alignment between the auditory and visual maps during normal visual experience, after the retinal image is shifted through prismatic goggles, and after the reestablishment of normal visual input. The results suggest that value-dependent learning is sufficient to account for the registration of auditory and visual maps of space in the OT of the barn owl, and they lead to a number of experimental predictions.
在仓鸮的视顶盖(OT)中,视觉和听觉空间图谱紧密排列。破坏这种排列的实验表明,听觉图谱具有相当程度的可塑性。下丘的外侧核(ICx)是大量投射到顶盖的听觉中枢,是可塑性的主要部位;然而,目前尚不清楚ICx中的听觉图谱与顶盖中的视觉图谱之间的排列是通过何种机制建立和维持的。在本文中,我们提出这种图谱排列是通过依赖价值的学习过程发生的。根据这一范式,价值系统可与具有弥散投射的神经调节系统相识别,对先天或后天的显著线索做出反应,并调节许多脑区突触效能的变化。为了检验这一假设的自洽性,我们开发了一个仓鸮听觉定位过程中主要神经结构的计算机模型。这通过对仓鸮表型和实验环境方面的模拟得到补充。在模型中,每当仓鸮对听觉刺激进行注视时,一个价值系统就会被激活。一个代表神经调质弥散释放的项与局部突触前和突触后事件相互作用,以确定ICx中的突触变化。通过大规模模拟,我们复制了一些关于在正常视觉体验期间、通过棱镜护目镜使视网膜图像移位后以及重新建立正常视觉输入后,听觉和视觉图谱之间空间排列发育的实验观察结果。结果表明,依赖价值的学习足以解释仓鸮视顶盖中听觉和视觉空间图谱的登记,并且它们导致了一些实验预测。