Stakhovskaya Olga, Sridhar Divya, Bonham Ben H, Leake Patricia A
Epstein Laboratory, Department of Otolaryngology-Head and Neck Surgery, University of California San Francisco, San Francisco, CA 94143-0526, USA.
J Assoc Res Otolaryngol. 2007 Jun;8(2):220-33. doi: 10.1007/s10162-007-0076-9. Epub 2007 Feb 21.
The goals of this study were to derive a frequency-position function for the human cochlear spiral ganglion (SG) to correlate represented frequency along the organ of Corti (OC) to location along the SG, to determine the range of individual variability, and to calculate an "average" frequency map (based on the trajectories of the dendrites of the SG cells). For both OC and SG frequency maps, a potentially important limitation is that accurate estimates of cochlear place frequency based upon the Greenwood function require knowledge of the total OC or SG length, which cannot be determined in most temporal bone and imaging studies. Therefore, an additional goal of this study was to evaluate a simple metric, basal coil diameter that might be utilized to estimate OC and SG length. Cadaver cochleae (n = 9) were fixed <24 h postmortem, stained with osmium tetroxide, microdissected, decalcified briefly, embedded in epoxy resin, and examined in surface preparations. In digital images, the OC and SG were measured, and the radial nerve fiber trajectories were traced to define a series of frequency-matched coordinates along the two structures. Images of the cochlear turns were reconstructed and measurements of basal turn diameter were made and correlated with OC and SG measurements. The data obtained provide a mathematical function for relating represented frequency along the OC to that of the SG. Results showed that whereas the distance along the OC that corresponds to a critical bandwidth is assumed to be constant throughout the cochlea, estimated critical band distance in the SG varies significantly along the spiral. Additional findings suggest that measurements of basal coil diameter in preoperative images may allow prediction of OC/SG length and estimation of the insertion depth required to reach specific angles of rotation and frequencies. Results also indicate that OC and SG percentage length expressed as a function of rotation angle from the round window is fairly constant across subjects. The implications of these findings for the design and surgical insertion of cochlear implants are discussed.
本研究的目的是推导人类耳蜗螺旋神经节（SG）的频率-位置函数，以将沿柯蒂氏器（OC）的表征频率与沿SG的位置相关联，确定个体变异性的范围，并计算一个“平均”频率图（基于SG细胞树突的轨迹）。对于OC和SG频率图，一个潜在的重要限制是，基于格林伍德函数对耳蜗位置频率的准确估计需要了解OC或SG的总长度，而在大多数颞骨和成像研究中无法确定该长度。因此，本研究的另一个目标是评估一个简单的指标——基底线圈直径，它可用于估计OC和SG的长度。将尸体耳蜗（n = 9）在死后<24小时固定，用四氧化锇染色，进行显微解剖，短暂脱钙，嵌入环氧树脂中，并在表面制备物中进行检查。在数字图像中，测量OC和SG，并追踪径向神经纤维轨迹，以定义沿这两个结构的一系列频率匹配坐标。重建耳蜗转弯的图像，测量基底转弯直径，并将其与OC和SG的测量值相关联。获得的数据提供了一个数学函数，用于将沿OC的表征频率与SG的频率相关联。结果表明，虽然在整个耳蜗中，对应于临界带宽的沿OC的距离被假定为恒定的，但SG中估计的临界带宽距离沿螺旋显著变化。其他研究结果表明，术前图像中基底线圈直径的测量可能有助于预测OC/SG长度，并估计达到特定旋转角度和频率所需的插入深度。结果还表明，以相对于圆窗的旋转角度表示的OC和SG百分比长度在不同受试者之间相当恒定。讨论了这些发现对人工耳蜗设计和手术植入的意义。
