Nakamoto Kyle T, Jones Simon J, Palmer Alan R
MRC Institute of Hearing Research, University Park, Nottingham, UK.
J Neurophysiol. 2008 May;99(5):2347-56. doi: 10.1152/jn.01326.2007. Epub 2008 Apr 2.
The function of the profuse descending innervation from the auditory cortex is largely unknown; however, recent studies have demonstrated that focal stimulation of auditory cortex effects frequency tuning curves, duration tuning, and other auditory parameters in the inferior colliculus. Here we demonstrate that, in an anesthetized guinea pig, nonfocal deactivation of the auditory cortex alters the sensitivity of populations of neurons in the inferior colliculus (IC) to one of the major cues for the localization of sound in space, interaural level differences (ILDs). Primary and secondary auditory cortical areas were inactivated by cooling. The ILD functions of 46% of IC cells changed when the cortex was inactivated. In extreme cases, the ILD functions changed from monotonic to nonmonotonic during cooling and vice versa. Eight percent of the cells became unresponsive after deactivation of the auditory cortex. Deactivation of the cortex has previously been shown to alter the maximum spike count of cells in the IC; the change in normalized ILD functions is shown to be separate from this effect. In some cases, the ILD function changed shape when there was no change in the maximum spike count and in other cases there was no change in the shape of the ILD function even though there was a large change in the maximum spike count. Overall, the sensitivity of the IC neural population to ILD is radically altered by the corticofugal pathway.
来自听觉皮层的大量下行神经支配的功能在很大程度上尚不清楚；然而，最近的研究表明，听觉皮层的局部刺激会影响下丘的频率调谐曲线、时长调谐及其他听觉参数。在此我们证明，在麻醉的豚鼠中，听觉皮层的非局部失活会改变下丘（IC）神经元群体对声音在空间中定位的主要线索之一——耳间水平差异（ILD）的敏感性。初级和次级听觉皮层区域通过冷却而失活。当皮层失活时，46%的IC细胞的ILD功能发生了变化。在极端情况下，冷却期间ILD功能从单调变为非单调，反之亦然。听觉皮层失活后，8%的细胞变得无反应。此前已表明皮层失活会改变IC中细胞的最大放电计数；归一化的ILD功能变化与这种效应是分开的。在某些情况下，当最大放电计数没有变化时，ILD功能会改变形状，而在其他情况下，即使最大放电计数有很大变化，ILD功能的形状也没有变化。总体而言，皮质传出通路会从根本上改变IC神经群体对ILD的敏感性。
