Journal Club: OCT vibrometry on the guinea pig cochlea; comparison between two separate methodologies

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Today's journal article

Chiriboga LA, Strimbu CE, Fallah E, Olson ES. Study of organ of Corti motion in the guinea pig base including differential analysis of internal motion. 

  • Hear Res. 2025 Oct 8;468:109449. 
  • doi: 10.1016/j.heares.2025.109449. 
  • Epub ahead of print. PMID: 41106088; PMCID: PMC12537013.
  • Available online at: https://www.sciencedirect.com/science/article/pii/S0378595525002679

Why I picked this article

The cochlea is an amazing sensing organ that can detect nanometer-range motion of the inner ear fluid. Sensitivity of the cochlea is further tuned and amplified by outer hair cells, sensory cells capable of responding to the sound-induced motion of the fluid, and then amplifying it by actively changing their cell lengths. However, how the outer hair elongation and shrinkage then contribute to amplified sensitivity of sound detection by inner hair cells is not clearly understood. 

Previous research has suggested some differences between the guinea pig cochlea and the gerbil cochlea in the way the sound triggers the motion of the outer hair cells and the basilar membrane underneath them. The present research focuses on the guinea pig cochlea to provide further evidence about this matter. 

Some of the research findings

Animal model:

  • Guinea pig (200-350g), both sex, juvernile
  • Middle ear space was exposed by opening the otic bullae
  • Measurement (OCT vibrometry) 

Setup:

  • Sound stimuli: RadioShack dynamic speaker was used to generate sound signals.
  • Sound stimuli: "Multitone zwuis stimuli containing 35 approximately equally spaced frequencies were presented for 1 s over a range of SPLs"
  • OCT vibrometry: Thorlabs Telesto OCT system with a center wavelength of 1300 nm with 5x objective lens.
  • Axis for movement: the optical axis of the Telesto system and the anatomical axes were related using the planar approximation method, to estimate the longitudinal, radial and transverse components. 
  • OCT vibrometry was done through:
    • basal cochleotomy - 
    • the round window - the optical axis was primarily transverse (0.85)
Key findings:
  • When measured through the round window, there was some non-linearity observed in the reticular lamina, or the top of the basilar membrane region. 
  • When measured through the round window, Outer hair cells showed similar movement to the basilar membrane.
  • When measured through a cochleostomy of a similar (basal) region, the outer hair cell region lagged from the basilar membrane region and showed amplification. 
Fig 3D OCT B-scan image of the guinea pig organ of Corti. Chiriboga et al. 2025.

Haruna's takeaway

Wow, very different observations were made by two separate approaches in conducting OCT vibrometry. It is very good that this research compared the two, with the same animal models and by the same research group. Authors further suggest that such a difference in approach, combined with the use of slightly different animal models (e.g., mice, gerbils and guinea pigs), is the likely cause of the current discrepancy. It is incredible that OCT vibrometry can provide insight into the basilar membrane motion at such resolution. Hopefully, with more studies like this combined with recent ex vivo OCT vibrometry studies, we will know the answers to all this soon. 

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This is Haruna's 74/100 of the 100-day challenge to post a science blog article every day! I love inner ear biology & cochlear physiology.