Cochlear mechanisms of frequency and intensity coding. I. The place code for pitch
1Institute for Sensory Research, Syracuse University, NY 13244, USA. monita@hei.org
Hearing Research
|November 5, 1997
Summary
A significant shift in the cochlear excitation pattern peak occurs with increasing sound pressure level (SPL). This study confirms this peak shift in inner hair cells (IHCs), challenging the classical place theory of hearing.
Area of Science:
- Auditory Neuroscience
- Cochlear Physiology
- Sensory Biology
Background:
- Previous studies indicate sound pressure level (SPL)-dependent shifts in cochlear excitation patterns.
- Evidence exists in auditory nerve fibers, cochlear microphonics, and outer hair cells, but direct inner hair cell (IHC) data is limited.
- Such shifts, if present in IHCs, necessitate modifications to the place theory of auditory frequency coding.
Purpose of the Study:
- To investigate the nature and extent of the SPL-dependent peak shift in the cochlea.
- To examine these shifts specifically in inner hair cells (IHCs) and other cochlear cells.
- To determine the implications for the place theory of pitch perception.
Main Methods:
- Recordings were made from inner hair cells (IHCs) and other cells within the organ of Corti.
- Experiments focused on the 0.5-2.5 kHz region of the Mongolian gerbil cochlea.
- Stimulating tones of varying sound pressure levels (SPLs) were used to evoke responses.
Main Results:
- A universal SPL-dependent peak shift was observed across diverse cell types in the studied cochlear region.
- Crucially, a significant SPL-dependent peak shift was demonstrated in inner hair cell (IHC) responses.
- The apical cutoff of the spatial excitation pattern was found to be independent of SPL.
Conclusions:
- The findings provide direct evidence for SPL-dependent peak shifts in inner hair cells (IHCs).
- The results indicate that the classical place theory of pitch perception requires modification or abandonment.
- The study highlights the complex mechanisms underlying frequency coding in the cochlea.
Related Concept Videos
01:31Hearing
When we hear a sound, our nervous system is detecting sound waves—pressure waves of mechanical energy traveling through a medium. The frequency of the wave is perceived as pitch, while the amplitude is perceived as loudness.
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.
01:13The 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.
00:53Sound Intensity Level
Humans perceive sound by hearing. The human ear helps sound waves reach the brain, which then interprets the waves and creates the perception of hearing. The loudness of the environment in which a person is located determines whether they can distinguish between different sound sources.
The human ear can perceive an extensive range of sound intensity, necessitating the use of the logarithmic scale to define a physical quantity—the intensity level. It is a ratio of two intensities and hence a...
The human ear can perceive an extensive range of sound intensity, necessitating the use of the logarithmic scale to define a physical quantity—the intensity level. It is a ratio of two intensities and hence a...
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...
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...