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A physiological frequency-position map of the chinchilla cochlea
Marcus Müller1, Silvi Hoidis, Jean W T Smolders
1Department of Neurophysiology, JW Goethe-Universität Frankfurt, Neuroscience Center, Theodor-Stern-Kai 7, D-60590 Frankfurt am Main, Germany. m.mueller@em.uni-frankfurt.de
Hearing Research
|August 6, 2010
Summary
Mammalian cochlear frequency maps shift with inner ear condition. Damage causes shifts to lower frequencies, altering vibration patterns. This study confirms physiological maps differ from anatomical maps in damaged ears.
Area of Science:
- Auditory Neuroscience
- Mammalian Cochlear Physiology
- Sensory System Mapping
Background:
- Mammalian cochlear frequency-position maps, crucial for hearing, are influenced by the inner ear's physiological state.
- Cochlear damage leads to desensitization, shifting the location of maximum basilar membrane vibration to lower frequencies for a given sound.
- This suggests frequency-position maps derived from damaged ears may inaccurately represent normal auditory function.
Purpose of the Study:
- To test the hypothesis that cochlear frequency-position maps are altered by inner ear condition.
- To compare frequency-position maps from healthy chinchillas with those from sound-overexposed ears.
- To investigate the impact of damage-induced desensitization on the basilar membrane vibration pattern.
Main Methods:
- Re-mapping the cochlear frequency-position map in chinchillas under normal physiological conditions.
- Comparing physiological map data with previously established anatomical maps from sound-overexposed ears.
- Determining characteristic frequencies (CF) of cochlear nucleus neurons and tracing auditory nerve fibers using HRP or biocytin.
Main Results:
- The relationship between distance from the base (d) and frequency (f) was described by d = 61.2 - 42.2 x log(f) with a slope of 2.55 mm/octave.
- The physiological map was shifted approximately 0.3 octaves to higher frequencies compared to the anatomical map.
- This corresponds to a 0.8 mm shift of the basilar membrane vibration pattern towards the apex for a given stimulus frequency.
Conclusions:
- Mammalian cochlear frequency-position maps are condition-dependent, varying with the inner ear's physiological state.
- Damage-induced desensitization causes shifts in CF and the vibration pattern's maximum location, influenced by species-specific mapping constants.
- The findings support the idea that low-frequency "crowding" in auditory processing may be a specialized adaptation.
Related Concept Videos
01:13The Cochlea
The cochlea is a coiled structure in the inner ear that contains hair cells—the sensory receptors of the auditory system. Sound waves are transmitted to the cochlea by small bones attached to the eardrum called the ossicles, which vibrate the oval window that leads to the inner ear. This causes fluid in the chambers of the cochlea to move, vibrating the basilar membrane.
01:22Hair Cells
Hair cells are the sensory receptors of the auditory system—they transduce mechanical sound waves into electrical energy that the nervous system can understand. Hair cells are located in the organ of Corti within the cochlea of the inner ear, between the basilar and tectorial membranes. The actual sensory receptors are called inner hair cells. The outer hair cells serve other functions, such as sound amplification in the cochlea, and are not discussed in detail here.
01:21Perceiving Loudness, Pitch, and Location
The human brain perceives pitch through two primary mechanisms reflected in place theory and frequency theory. Each mechanism describes how sound waves are interpreted as specific pitches by the brain, offering insights into the intricate processes of auditory perception.
Place theory, or place coding, suggests that different pitches are heard because various sound waves activate specific locations along the cochlea's basilar membrane. The brain determines the pitch of a sound by identifying...
Place theory, or place coding, suggests that different pitches are heard because various sound waves activate specific locations along the cochlea's basilar membrane. The brain determines the pitch of a sound by identifying...
01:16Anatomy of the Ear
Auditory sensation, commonly called hearing, involves the transformation of sonic waves into neural impulses facilitated by the structures of the auditory organ. The prominent, flesh-like structure on the side of the head, called the auricle, directs sound waves towards the auditory canal. The auricle is often mislabeled as the pinna, a term more aligned with mobile structures like a feline's external ear. The auditory canal penetrates the cranium via the external auditory meatus of the...
01:15Auditory Pathway
Auditory pathways constitute the complex neural circuits responsible for transmitting and interpreting auditory information from the peripheral auditory system to the brain. Sound waves are initially captured by the outer ear, funneled through the ear canal, and reach the tympanic membrane (eardrum). These vibrations are transmitted via the middle ear's ossicles to the inner ear's cochlea.
When viewed cross-sectionally, the cochlea reveals the scala vestibuli and scala tympani flanking the...
When viewed cross-sectionally, the cochlea reveals the scala vestibuli and scala tympani flanking the...