King Andrew J, Bajo Victoria M, Bizley Jennifer K, Campbell Robert A A, Nodal Fernando R, Schulz Andreas L, Schnupp Jan W H
Department of Physiology, Anatomy and Genetics, Sherrington Building, University of Oxford, Oxford, UK.
Hear Res. 2007 Jul;229(1-2):106-15. doi: 10.1016/j.heares.2007.01.001. Epub 2007 Jan 17.
Despite extensive subcortical processing, the auditory cortex is believed to be essential for normal sound localization. However, we still have a poor understanding of how auditory spatial information is encoded in the cortex and of the relative contribution of different cortical areas to spatial hearing. We investigated the behavioral consequences of inactivating ferret primary auditory cortex (A1) on auditory localization by implanting a sustained release polymer containing the GABA(A) agonist muscimol bilaterally over A1. Silencing A1 led to a reversible deficit in the localization of brief noise bursts in both the horizontal and vertical planes. In other ferrets, large bilateral lesions of the auditory cortex, which extended beyond A1, produced more severe and persistent localization deficits. To investigate the processing of spatial information by high-frequency A1 neurons, we measured their binaural-level functions and used individualized virtual acoustic space stimuli to record their spatial receptive fields (SRFs) in anesthetized ferrets. We observed the existence of a continuum of response properties, with most neurons preferring contralateral sound locations. In many cases, the SRFs could be explained by a simple linear interaction between the acoustical properties of the head and external ears and the binaural frequency tuning of the neurons. Azimuth response profiles recorded in awake ferrets were very similar and further analysis suggested that the slopes of these functions and location-dependent variations in spike timing are the main information-bearing parameters. Studies of sensory plasticity can also provide valuable insights into the role of different brain areas and the way in which information is represented within them. For example, stimulus-specific training allows accurate auditory localization by adult ferrets to be relearned after manipulating binaural cues by occluding one ear. Reversible inactivation of A1 resulted in slower and less complete adaptation than in normal controls, whereas selective lesions of the descending cortico collicular pathway prevented any improvement in performance. These results reveal a role for auditory cortex in training-induced plasticity of auditory localization, which could be mediated by descending cortical pathways.
尽管存在广泛的皮层下处理过程，但听觉皮层被认为对于正常的声音定位至关重要。然而，我们对听觉空间信息在皮层中如何编码以及不同皮层区域对空间听觉的相对贡献仍知之甚少。我们通过在雪貂初级听觉皮层（A1）双侧植入含有GABA(A)激动剂蝇蕈醇的缓释聚合物，研究了灭活A1对听觉定位的行为后果。使A1沉默导致在水平和垂直平面上短暂噪声脉冲定位出现可逆性缺陷。在其他雪貂中，超出A1范围的双侧听觉皮层大损伤产生了更严重和持久的定位缺陷。为了研究高频A1神经元对空间信息的处理，我们测量了它们的双耳水平功能，并使用个性化的虚拟声学空间刺激在麻醉的雪貂中记录它们的空间感受野（SRF）。我们观察到存在一系列连续的反应特性，大多数神经元偏好对侧声音位置。在许多情况下，SRF可以通过头部和外耳的声学特性与神经元的双耳频率调谐之间的简单线性相互作用来解释。在清醒雪貂中记录的方位角反应曲线非常相似，进一步分析表明这些函数的斜率和与位置相关的尖峰时间变化是主要的信息承载参数。感觉可塑性的研究也可以为不同脑区的作用以及信息在其中的表示方式提供有价值的见解。例如，特定刺激训练使成年雪貂在通过堵塞一只耳朵操纵双耳线索后能够重新学习准确的听觉定位。与正常对照组相比，A1的可逆性失活导致适应更慢且更不完全，而皮质-丘系下行通路的选择性损伤则阻止了性能的任何改善。这些结果揭示了听觉皮层在训练诱导的听觉定位可塑性中的作用，这可能由皮质下行通路介导。
