Dobrev Ivo, Ihrle Sebastian, Röösli Christof, Gerig Rahel, Eiber Albrecht, Huber Alexander M, Sim Jae Hoon
University Hospital Zurich, University of Zurich, Zurich, Switzerland.
University of Stuttgart, Stuttgart, Germany.
Hear Res. 2016 Oct;340:89-98. doi: 10.1016/j.heares.2015.10.016. Epub 2015 Dec 2.
The malleus-incus complex (MIC) plays a crucial role in the hearing process as it transforms and transmits acoustically-induced motion of the tympanic membrane, through the stapes, into the inner-ear. However, the transfer function of the MIC under physiologically-relevant acoustic stimulation is still under debate, especially due to insufficient quantitative data of the vibrational behavior of the MIC. This study focuses on the investigation of the sound transformation through the MIC, based on measurements of three-dimensional motions of the malleus and incus with a full six degrees of freedom (6 DOF).
The motion of the MIC was measured in two cadaveric human temporal bones with intact middle-ear structures excited via a loudspeaker embedded in an artificial ear canal, in the frequency range of 0.5-5 kHz. Three-dimensional (3D) shapes of the middle-ear ossicles were obtained by sequent micro-CT imaging, and an intrinsic frame based on the middle-ear anatomy was defined. All data were registered into the intrinsic frame, and rigid body motions of the malleus and incus were calculated with full six degrees of freedom. Then, the transfer function of the MIC, defined as velocity of the incus lenticular process relative to velocity of the malleus umbo, was obtained and analyzed.
Based on the transfer function of the MIC, the motion of the lenticularis relative to the umbo reduces with frequency, particularly in the 2-5 kHz range. Analysis of the individual motion components of the transfer function indicates a predominant medial-lateral component at frequencies below 1 kHz, with low but considerable anterior-posterior and superior-inferior components that become prominent in the 2-5 kHz range.
The transfer function of the human MIC, based on motion of the umbo and lenticularis, has been visualized and analyzed. While the magnitude of the transfer function decreases with frequency, its spatio-temporal complexity increases significantly.
锤骨 - 砧骨复合体（MIC）在听力过程中起着关键作用，它将鼓膜的声学诱导运动通过镫骨转化并传递到内耳。然而，在生理相关声学刺激下MIC的传递函数仍存在争议，特别是由于MIC振动行为的定量数据不足。本研究基于对锤骨和砧骨六自由度（6 DOF）三维运动的测量，重点研究通过MIC的声音转换。
在两只中耳结构完整的尸体人类颞骨中测量MIC的运动，通过嵌入人工耳道的扬声器在0.5 - 5 kHz频率范围内激发。通过连续的微型计算机断层扫描成像获得中耳听小骨的三维（3D）形状，并基于中耳解剖结构定义一个固有框架。所有数据都注册到固有框架中，并计算锤骨和砧骨的刚体六自由度运动。然后，获得并分析MIC的传递函数，其定义为砧骨豆状突速度相对于锤骨柄速度。
基于MIC的传递函数，豆状突相对于锤骨柄的运动随频率降低，特别是在2 - 5 kHz范围内。对传递函数的各个运动分量的分析表明，在1 kHz以下频率，主要是内外侧分量，而前后和上下分量较低但相当可观，在2 - 5 kHz范围内变得突出。
基于锤骨柄和豆状突运动的人类MIC传递函数已得到可视化和分析。虽然传递函数的幅度随频率降低，但其时空复杂性显著增加。
