Fig. 8 | Nature Communications

Fig. 8

From: Vibration hotspots reveal longitudinal funneling of sound-evoked motion in the mammalian cochlea

Fig. 8

Viewing-angle dependent ‘relative-phase inversion’ of hotspot motion. a Contrast between the purely transverse motion of the BM (vertical arrows) and the elliptical trajectories predicted for fluid (and potentially structural) particles underlying a surface wave in the cochlea1, 38, 39, 68. The wave’s surface (the BM, black line) is pictured at two instants in time, separated by 1/8 cycle, with neighboring fluid particle trajectories shown (using dashed blue lines) at two longitudinal positions. Coordinates: x = longitudinal; z = transverse. Longer wavelengths correspond to more elongated ellipses. The illustrated tilt of the ellipse (θ in b) may result from dissipation in either the fluids39, 68 or structures within the organ of Corti (see Supplementary Note 3). b, c Predicted effects of viewing angle on measured motion. In b, a “negative” angle α1 views the wave traveling away from the measurement beam, with the measured (projected) motion of the ellipse phase-leading the transverse motion of the BM. By contrast, a “positive” viewing angle α2 observes the same wave as traveling towards the beam, such that the measured motion of the ellipse phase-lags the transverse BM motion. c Exemplar relationships between viewing angle and the relative phase of the projected motion for ellipses with 10-degrees of baseline tilt (θ, see b) and longitudinal/transverse elongation factors of 1, 3, and 10 (see key). Computations, see Supplementary Note 4. d OCT image from one of two preparations where vibration measurements were made from positive angles of incidence (α2 in b). Scale bar, 0.025 mm. e Profiles of vibration amplitude across the path shown by the red arrow in d. Each curve represents one frequency component in the multi-tone stimulus. Four specific frequencies are identified by increased line width: 5.7 kHz (green), 10.6 kHz (black), 17.2 kHz (red), and 37.2 kHz (blue). f Corresponding phase data. All profiles are referenced to the vibrations observed at the BM location indicated with a white star in d. Gray patches indicate the different regions traversed by the red arrow, including the BM, Deiters’ cells (DC) and OHCs (marked by the black triangle). Preparation RG16760, CF 40 kHz. Stimulus level 60 dB SPL