Tonotopic organization of the auditory cortex: pitch versus frequency representation
Article Abstract:
The precise functioning of the auditory cortex, the area of the brain believed to be responsible for processing sound waves, is not completely understood. The two traditional hypotheses are somewhat contradictory. The first theory, called tonotopic organization, involves the use of a system of spatial relationships where the brain processes tones according to their frequencies. The perceived pitch is believed to be directly related to the area of the brain that is stimulated. However, the second theory is based on the observation that pitch composed of complex tones containing various frequencies creates a pattern similar to a pure tone. To further explore the two hypotheses, biomagnetic measurements were performed using auditory-evoked magnetic fields (AEF) in an effort to better understand how the brain processes complex tones. AEFs provide a good spatial resolution and reveal the tonotopic organization of the primary auditory cortex in humans. A pure tone stimulus (spectral pitch) and a complex-tone stimulus (virtual pitch) were measured and compared using three different stimulus signals. Two bursts of pure tone, with frequencies of 250Hz and 1,000Hz, were measured, along with a strong varying virtual pitch. When the complex-tone signal was measured in 15 individuals and compared to the patterns of the two spectral pitches, it was found to match up with the pattern exhibited by the 250Hz pure-tone stimulus. Researchers concluded that the pitch of the stimulus, but not the actual frequencies, is reflected in the tonotopic organization of the primary auditory cortex. Therefore, it was hypothesized that the actual process of pitch formation takes place in subcortical regions of the brain. The results also provide a method of neurological mapping for complex and simple tones for use in subsequent research in this area.
Publication Name: Science
Subject: Science and technology
ISSN: 0036-8075
Year: 1989
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The Benefits of Recycling
Article Abstract:
The sensory hair cells, located in the cochlea of the inner ear, convert sound waves into electrical impulses. Research indicates that a recycling process that takes place in the coclear duct is important to hearing. In addition, the loss of a portein that helps maintain the hair cells can cause a progressive hearing loss.
Publication Name: Science
Subject: Science and technology
ISSN: 0036-8075
Year: 1999
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Making Brain Circuits Listen
Article Abstract:
Research on the auditory cortex of animals is discussed. The new research convincingly shows that the auditory cortical map can be extended on deaf kittens by electrical stimulation of their auditory nerves. Included is an explanation of how the research was conducted.
Publication Name: Science
Subject: Science and technology
ISSN: 0036-8075
Year: 1999
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