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Tonotopic Representation (tonotopic + representation)

Distribution by Scientific Domains

Life Sciences	100%

Selected Abstracts

Tonotopic representation of missing fundamental complex sounds in the human auditory cortex

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 2 2003
Takako Fujioka
Abstract The N1m component of the auditory evoked magnetic field in response to tones and complex sounds was examined in order to clarify whether the tonotopic representation in the human secondary auditory cortex is based on perceived pitch or the physical frequency spectrum of the sound. The investigated stimulus parameters were the fundamental frequencies (F0 = 250, 500 and 1000 Hz), the spectral composition of the higher harmonics of the missing fundamental sounds (2nd to 5th, 6th to 9th and 10th to 13th harmonic) and the frequencies of pure tones corresponding to F0 and to the lowest component of each complex sound. Tonotopic gradients showed that high frequencies were more medially located than low frequencies for the pure tones and for the centre frequency of the complex tones. Furthermore, in the superior,inferior direction, the tonotopic gradients were different between pure tones and complex sounds. The results were interpreted as reflecting different processing in the auditory cortex for pure tones and complex sounds. This hypothesis was supported by the result of evoked responses to complex sounds having longer latencies. A more pronounced tonotopic representation in the right hemisphere gave evidence for right hemispheric dominance in spectral processing. [source]

Connections of functional areas in the mustached bat's auditory cortex with the auditory thalamus

THE JOURNAL OF COMPARATIVE NEUROLOGY, Issue 2 2007
James M. Pearson
Abstract The auditory thalamus is the major target of the inferior colliculus and connects in turn with the auditory cortex. In the mustached bat, biosonar information is represented according to frequency in the central nucleus of the inferior colliculus (ICc) but according to response type in the cortex. In addition, the cortex has multiple areas with neurons of similar response type compared to the single tonotopic representation in the ICc. To investigate whether these transformations occur at the level of the thalamus, we injected anatomical tracers into physiologically defined locations in the mustached bat's auditory cortex. Injections in areas used for target ranging labeled contiguous regions of the auditory thalamus rather than separate patches corresponding to regions that respond to the different harmonic frequencies used for ranging. Injections in the two largest ranging areas produced labeling in separate locations. These results indicate that the thalamus is organized according to response type rather than frequency and that multiple mappings of response types exist. Injections in areas used for target detection labeled thalamic regions that were largely separate from those that interconnect with ranging areas. However, injections in an area used for determining target velocity overlapped with the areas connected to ranging areas and areas involved in target detection. Thus, separation by functional type and multiplication of areas with similar response type occurs by the thalamic level, but connections with the cortex segregate the functional types more completely than occurs in the thalamus. J. Comp. Neurol. 500:401,418, 2007. © 2006 Wiley-Liss, Inc. [source]