Pérez M Lucía, Shanbhag Sharad J, Peña José Luis
Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Rose F. Kennedy Center, Rm. 529, 1410 Pelham Pkwy. S., Bronx, NY 10461, USA.
J Neurophysiol. 2009 Sep;102(3):1472-82. doi: 10.1152/jn.00400.2009. Epub 2009 Jul 1.
The barn owl's midbrain and forebrain contain neurons tuned to sound direction. The spatial receptive fields of these neurons result from sensitivity to combinations of interaural time (ITD) and level (ILD) differences over a broad frequency range. While a map of auditory space has been described in the midbrain, no similar topographic representation has been found in the forebrain. The first nuclei that belong exclusively to the forebrain and midbrain pathways are the thalamic nucleus ovoidalis (Ov) and the external nucleus of the inferior colliculus (ICx), respectively. The midbrain projects to the auditory thalamus before sharp spatial receptive fields emerge; although Ov and ICx receive projections from the same midbrain nuclei, they are not directly connected. We compared the spatial tuning in Ov and ICx. Thalamic neurons respond to a broader frequency range and their ITD and ILD tuning varied more across frequency. However, neurons in Ov showed spatial receptive fields as selective as neurons in ICx. Thalamic spatial receptive fields were tuned to frontal and contralateral space and correlated with their tuning to ITD and ILD. Our results indicate that spatial tuning emerges in both pathways by similar combination selectivity to ITD and ILD. However, the midbrain and the thalamus do not appear to repeat exactly the same processing, as indicated by the difference in frequency range and the broader tuning to binaural cues. The differences observed at the initial stages of these sound-localization pathways may reflect diverse functions and coding schemes of midbrain and forebrain.
仓鸮的中脑和前脑包含对声音方向进行调谐的神经元。这些神经元的空间感受野源于在很宽的频率范围内对双耳时间(ITD)和强度(ILD)差异组合的敏感性。虽然中脑中已描述了听觉空间图谱,但在前脑中未发现类似的拓扑表征。分别专门属于前脑和中脑通路的首批核团是丘脑卵圆核(Ov)和下丘外侧核(ICx)。在尖锐的空间感受野出现之前,中脑投射到听觉丘脑;尽管Ov和ICx接受来自相同中脑核团的投射,但它们并不直接相连。我们比较了Ov和ICx中的空间调谐。丘脑神经元对更宽的频率范围做出反应,并且它们的ITD和ILD调谐在频率上变化更大。然而,Ov中的神经元表现出与ICx中的神经元一样具有选择性的空间感受野。丘脑空间感受野被调谐到额叶和对侧空间,并与其对ITD和ILD的调谐相关。我们的结果表明,通过对ITD和ILD的类似组合选择性,两条通路中都出现了空间调谐。然而,中脑和丘脑似乎并未完全重复相同的处理过程,这从频率范围的差异以及对双耳线索更宽泛的调谐中可以看出。在这些声音定位通路的初始阶段观察到的差异可能反映了中脑和前脑的不同功能和编码方案。