Department of Physiology, Anatomy and Genetics, University of Oxford Oxford, UK.
Front Neuroanat. 2010 May 21;4:18. doi: 10.3389/fnana.2010.00018. eCollection 2010.
Descending cortical inputs to the superior colliculus (SC) contribute to the unisensory response properties of the neurons found there and are critical for multisensory integration. However, little is known about the relative contribution of different auditory cortical areas to this projection or the distribution of their terminals in the SC. We characterized this projection in the ferret by injecting tracers in the SC and auditory cortex. Large pyramidal neurons were labeled in layer V of different parts of the ectosylvian gyrus after tracer injections in the SC. Those cells were most numerous in the anterior ectosylvian gyrus (AEG), and particularly in the anterior ventral field, which receives both auditory and visual inputs. Labeling was also found in the posterior ectosylvian gyrus (PEG), predominantly in the tonotopically organized posterior suprasylvian field. Profuse anterograde labeling was present in the SC following tracer injections at the site of acoustically responsive neurons in the AEG or PEG, with terminal fields being both more prominent and clustered for inputs originating from the AEG. Terminals from both cortical areas were located throughout the intermediate and deep layers, but were most concentrated in the posterior half of the SC, where peripheral stimulus locations are represented. No inputs were identified from primary auditory cortical areas, although some labeling was found in the surrounding sulci. Our findings suggest that higher level auditory cortical areas, including those involved in multisensory processing, may modulate SC function via their projections into its deeper layers.
皮质下行传入至上丘（SC）有助于那里发现的神经元的单感觉反应特性，并对多感觉整合至关重要。然而，对于不同听觉皮质区域对该投射的相对贡献，或者它们在 SC 中的终末分布，知之甚少。我们通过在 SC 和听觉皮质中注射示踪剂，在雪貂中描述了这种投射。在 SC 内注射示踪剂后，在不同外 Sylvius 回叶的 V 层中标记了大型锥体神经元。这些细胞在前外 Sylvius 回（AEG）中数量最多，特别是在前腹侧场，该场接收听觉和视觉输入。在外 Sylvius 回的后区（PEG）也发现了标记，主要在听觉组织的后上 Sylvius 场。在外 Sylvius 回的 AEG 或 PEG 中，在对声音有反应的神经元部位注射示踪剂后，SC 中出现了大量的顺行标记，其终末场对于来自 AEG 的输入更为突出和聚集。来自两个皮质区域的终末位于中间和深层，但在 SC 的后半部分最为集中，在那里代表外周刺激位置。尽管在周围的脑沟中发现了一些标记，但未从初级听觉皮质区域识别出输入。我们的发现表明，包括参与多感觉处理的高级听觉皮质区域，可能通过其投射到 SC 的深层来调节 SC 的功能。
