Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI, USA.
Bioessays. 2023 Aug;45(8):e2300058. doi: 10.1002/bies.202300058. Epub 2023 Jun 17.
A ubiquitous feature of the auditory organ in amniotes is the longitudinal mapping of neuronal characteristic frequencies (CFs), which increase exponentially with distance along the organ. The exponential tonotopic map reflects variation in hair cell properties according to cochlear location and is thought to stem from concentration gradients in diffusible morphogenic proteins during embryonic development. While in all amniotes the spatial gradient is initiated by sonic hedgehog (SHH), released from the notochord and floorplate, subsequent molecular pathways are not fully understood. In chickens, BMP7 is one such morphogen, secreted from the distal end of the cochlea. In mammals, the developmental mechanism differs from birds and may depend on cochlear location. A consequence of exponential maps is that each octave occupies an equal distance on the cochlea, a spacing preserved in the tonotopic maps in higher auditory brain regions. This may facilitate frequency analysis and recognition of acoustic sequences.
羊膜动物听觉器官的一个普遍特征是神经元特征频率 (CFs) 的纵向映射，该频率随着器官的距离呈指数增长。指数音调图反映了根据耳蜗位置的毛细胞特性的变化，据认为它源自胚胎发育过程中扩散形态发生蛋白的浓度梯度。虽然在所有羊膜动物中，空间梯度都是由 Sonic Hedgehog (SHH) 启动的，SHH 从脊索和基板释放，但随后的分子途径尚不完全清楚。在鸡中，BMP7 就是这样一种形态发生素，从耳蜗的远端分泌。在哺乳动物中，发育机制与鸟类不同，可能取决于耳蜗的位置。指数映射的一个结果是，每个八度占据耳蜗上相等的距离，这种间隔在较高听觉脑区的音调图中得以保留。这可能有助于频率分析和声音序列的识别。
