Thiele A, Rübsamen R, Hoffmann K P
Ruhr-Universität Bochum, Germany.
Exp Brain Res. 1996 Nov;112(2):223-36. doi: 10.1007/BF00227641.
The objective of this study was to investigate whether a representation of auditory space in the superior colliculus (SC) of the echolocating megachiropteran bat (Rousettus aegyptiacus) exists. Additionally the subcortical auditory connectivity of the SC was investigated. A total of 207 units were recorded in five awake animals while presenting acoustic stimuli (white noise, clicks, and pure tones) at different positions in space. Six units responded to acoustic stimulation. Three of these located within the superficial layers and one located in the intermediate layers were classified as omnidirectional units. Two units were located within the deep layers. One was classified as a hemifield unit, and the other as a frontal unit. All units responded phasically to acoustic stimulation with a latency of 4-150 ms. None of them could be activated by visual stimuli. We further examined the interaction of paired auditory and visual stimulation in 116 visually responsive units. Responses to visual stimulation were markedly altered by acoustic stimulation in 5 units. The influence of the acoustic stimuli was temporally and spatially restricted, and resulted either in a reduction or an elevation of unit responsiveness. Horseradish peroxidase was injected into the SC of eight animals to investigate the auditory subcortical connectivity of the SC. Retrograde labeling in auditory structures was rare compared with labeling found in nonauditory structures (e.g., retina, substantia nigra, parabigeminal nucleus). In auditory structures retrograde labeling was found mainly in the external nucleus of the inferior colliculus and in the nucleus of the brachium of the inferior colliculus. To a lesser extent it was found in the nucleus sagulum and in the area medial to the lemniscal nuclei. In one case the dorsal nucleus of the lateral lemniscus and the anterolateral periolivary nucleus were labeled. Our results reveal only a sparse auditory input into the SC of the flying fox, R. aegyptiacus. On the basis of single-unit recordings, we did not find an elaborate representation of auditory space as it is described for several other species. The existence of auditory and bimodal neurones, in combination with their response properties, nonetheless indicate that there might be a representation of auditory space in the SC of R. aegyptiacus.
本研究的目的是调查回声定位的大型翼手目蝙蝠（埃及果蝠）上丘（SC）中是否存在听觉空间表征。此外，还研究了上丘的皮质下听觉连接。在5只清醒动物中记录了总共207个神经元，同时在空间中的不同位置呈现声学刺激（白噪声、点击声和纯音）。6个神经元对声学刺激有反应。其中3个位于浅层，1个位于中层，被归类为全向神经元。2个神经元位于深层。1个被归类为半视野神经元，另一个为额叶神经元。所有神经元对声学刺激均产生相位反应，潜伏期为4 - 150毫秒。它们均不能被视觉刺激激活。我们进一步检查了116个视觉反应性神经元中配对听觉和视觉刺激的相互作用。在5个神经元中，声学刺激显著改变了对视觉刺激的反应。声学刺激的影响在时间和空间上受到限制，导致神经元反应性降低或升高。将辣根过氧化物酶注入8只动物的上丘，以研究上丘的听觉皮质下连接。与在非听觉结构（如视网膜、黑质、副视束核）中发现的标记相比，听觉结构中的逆行标记很少。在听觉结构中，逆行标记主要在下丘的外侧核和下丘臂核中发现。在较小程度上，在矢状核和内侧丘系核内侧区域中发现。在1例中，外侧丘系背核和橄榄周前外侧核被标记。我们的结果表明，埃及果蝠上丘的听觉输入稀疏。基于单神经元记录，我们没有发现像其他几个物种那样精细的听觉空间表征。然而，听觉和双模式神经元的存在及其反应特性表明，埃及果蝠的上丘中可能存在听觉空间表征。
