Re: pitch neurons (Israel Nelken )

Subject: Re: pitch neurons
From:    Israel Nelken  <israel(at)MD.HUJI.AC.IL>
Date:    Wed, 2 Oct 2002 11:03:26 +0100

Dear Martin and List, Dave McAlpine presented a poster at ARO (2002, asbtract no. 154) in which he suggests (rather convincingly, IMHO) that the responses to high-carrier sinusoidally-modulated tones (HC-SAMs) are due to cochlear combination tones. The discussion in the Biebel and Langner paper does not addresses, but not really answer, this critique. It's the other piece of evidence that they bring (very wide inhibitory sidebands) that is for me the more convincing evidence for wide-band integration by these neurons, but then such wide bandwidth can already be demonstrated in the dorsal cochlear nucleus (e.g. Spirou and Young, J Neurophysiol. 1991 Nov;66(5):1750-68 and Spirou et al., J Neurophysiol. 1999 Aug;82(2):648-63) which is an important input to the inferior colliculus. Another piece of evidence against the interpretation of responses to HC-SAMs as related to pitch comes from some optical imaging results that we recently collected in ferret auditory cortex (to be presented at the Neuroscience meeting in Orlando, FL in November). We used HC-SAMs with a carrier at 6 kHz, that produce essentially no pitch sensation, and also high-pass clicks (at 4 kHz, with rather shallow slope) that do produce a very strong pitch perception. We demonstrated a response in low-frequency AI that was sensitive to the modulation frequency of the HC-SAM, but was insensitive to the period of the high-passed clicks. This result essentially reproduces the data of Schultze et al. (Eur. J. Neurosci. 15:1077-1084, 2002) who showed activation of low-frequency auditory cortex by HC-SAM in gerbils, but the additional test using high-passed clicks is a serious reason to doubt the interpretation of this map as related to pitch. All in all, I think that the cautious position at the moment is still that there is no unequivocal evidence for pitch sensitivity up to and including the level of primary auditory cortex in animals, independent of the spectral content of the sounds. Eli -- ================================================================== Israel Nelken | Tel: Int-44-1865-272438 Dept. of Physiology, | Fax: Int-44-1865-272469 Hebrew University - | Hadassah Medical School | P.O.Box 12272, Jerusalem 91120 | Email:israel(at) ISRAEL | ==================================================================

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