Homma Natsumi Y, Happel Max F K, Nodal Fernando R, Ohl Frank W, King Andrew J, Bajo Victoria M
Department of Physiology, Anatomy, and Genetics, University of Oxford, Oxford OX1 3PT, United Kingdom, and.
Department of Systems Physiology of Learning, Leibniz Institute for Neurobiology, D-39118 Magdeburg, Germany.
J Neurosci. 2017 Jun 21;37(25):6149-6161. doi: 10.1523/JNEUROSCI.0397-17.2017. Epub 2017 May 30.
Feedback signals from the primary auditory cortex (A1) can shape the receptive field properties of neurons in the ventral division of the medial geniculate body (MGBv). However, the behavioral significance of corticothalamic modulation is unknown. The aim of this study was to elucidate the role of this descending pathway in the perception of complex sounds. We tested the ability of adult female ferrets to detect the presence of a mistuned harmonic in a complex tone using a positive conditioned go/no-go behavioral paradigm before and after the input from layer VI in A1 to MGBv was bilaterally and selectively eliminated using chromophore-targeted laser photolysis. MGBv neurons were identified by their short latencies and sharp tuning curves. They responded robustly to harmonic complex tones and exhibited an increase in firing rate and temporal pattern changes when one frequency component in the complex tone was mistuned. Injections of fluorescent microbeads conjugated with a light-sensitive chromophore were made in MGBv, and, following retrograde transport to the cortical cell bodies, apoptosis was induced by infrared laser illumination of A1. This resulted in a selective loss of ∼60% of layer VI A1-MGBv neurons. After the lesion, mistuning detection was impaired, as indicated by decreased ' values, a shift of the psychometric curves toward higher mistuning values, and increased thresholds, whereas discrimination performance was unaffected when level cues were also available. Our results suggest that A1-MGBv corticothalamic feedback contributes to the detection of harmonicity, one of the most important grouping cues in the perception of complex sounds. Perception of a complex auditory scene is based on the ability of the brain to group those sound components that belong to the same source and to segregate them from those belonging to different sources. Because two people talking simultaneously may differ in their voice pitch, perceiving the harmonic structure of sounds is very important for auditory scene analysis. Here we demonstrate mistuning sensitivity in the thalamus and that feedback from the primary auditory cortex is required for the normal ability of ferrets to detect a mistuned harmonic within a complex sound. These results provide novel insight into the function of descending sensory pathways in the brain and suggest that this corticothalamic circuit plays an important role in scene analysis.
来自初级听觉皮层（A1）的反馈信号能够塑造内侧膝状体腹侧部（MGBv）神经元的感受野特性。然而，皮质丘脑调制的行为学意义尚不清楚。本研究的目的是阐明这条下行通路在复杂声音感知中的作用。我们采用阳性条件性Go/No-Go行为范式，在使用发色团靶向激光光解双侧选择性消除A1第VI层到MGBv的输入之前和之后，测试成年雌性雪貂检测复杂音调中失谐谐波存在的能力。MGBv神经元通过其短潜伏期和尖锐的调谐曲线来识别。它们对谐波复合音调有强烈反应，并且当复合音调中的一个频率成分失谐时，其放电率增加且时间模式发生变化。将与光敏发色团偶联的荧光微珠注射到MGBv中，在逆行运输到皮层细胞体后，通过A1的红外激光照射诱导细胞凋亡。这导致约60%的第VI层A1-MGBv神经元选择性丧失。损伤后，失谐检测受损，表现为“值”降低、心理测量曲线向更高失谐值偏移以及阈值增加，而当也有强度线索时，辨别性能不受影响。我们的结果表明，A1-MGBv皮质丘脑反馈有助于谐波性的检测，谐波性是复杂声音感知中最重要的分组线索之一。对复杂听觉场景的感知基于大脑将属于同一声源的那些声音成分分组并将它们与属于不同声源的成分区分开来的能力。因为两个人同时说话时音高可能不同，所以感知声音的谐波结构对于听觉场景分析非常重要。在这里，我们证明了丘脑的失谐敏感性，并且初级听觉皮层的反馈是雪貂在复杂声音中检测失谐谐波的正常能力所必需的。这些结果为大脑中下行感觉通路的功能提供了新的见解，并表明这条皮质丘脑回路在场景分析中起重要作用。
