Development of sound frequency representation in auditory cortex of chinchilla.
Published: 2004
Language: eng
Number of pages: 94
Description: Sensory neural pathways develop through a combination of "pre-wiring" by innate processes and "re-wiring" by the external environment ("nature and nurture"). However, there is increasing evidence that the development of the systematic (topographic) representation of receptor space in the visual pathway (retinotopic map) does not require external light, but rather gradients of chemical markers and waves of spontaneous activity. Is the same true of the development of topographic sound frequency (tonotopic) maps in the auditory pathway?Single-unit responses to tone pip stimuli were isolated from numerous microelectrode penetrations of auditory cortex (under ketamine anesthesia) in the developing chinchilla (laniger), a precocious mammal. Results are reported at postnatal day 3 (P3), P15, P30 and from adult animals. Hearing sensitivity and spike firing rates were mature in the youngest group. Tonotopic maps in primary and secondary auditory cortex were also well-ordered and sharply tuned by P3. The representation of sound frequency in the chinchilla auditory pathway thus appears to reach maturity in utero, where external (and maternal) sounds are considerably attenuated, and might not contribute to the mechanism(s) involved.On the other hand, the spectral-temporal complexity of cortical receptive fields increased progressively (past P30) to adulthood. Increasing fractions of neurons responded to multiple frequency bands, distinct in space and/or time. This likely reflects the continuing postnatal emergence of lateral connections between cortical columns, perhaps to confer selectivity for recurring fragments of species-specific vocalizations, such as frequency stacks and glides.There are several key parallels in the timelines of chinchilla and human auditory system development. It may be, therefore, that inadequate sound stimulation in early infancy (e.g. due to chronic middle ear disease) does not affect the sensorineural machinery required for precise frequency resolution, but may prevent the emergence of more complex sound feature selectivity, and so contribute to impaired speech perception.
Notes: Adviser:  Robert V. Harrison.

Thesis (Ph.D.)--University of Toronto, 2004.

Electronic version licensed for access by U. of T. users.

Source: Dissertation Abstracts International, Volume: 65-10, Section: B, page: 5017.