pitch in primate auditory cortex

[Martin Braun <nombraun@xxxxxxxxx>]

John Bates wrote:

> ..... I refer to "The neuronal representation of pitch in primate auditory
> cortex." by Daniel Bendor and Xiaoqin Wang in the August 25 issue of
> Nature. They demonstrate that the missing fundamental is a valid neural
> percept .........

Pitch neurons had previously been recorded in the auditory midbrain, i.e. 
two synaptic levels below the primary auditory cortex, by Biebel and Langner 
(1997 and 2002). The new findings of Bendor and Wang agree well with the 
earlier ones, and they provide an important missing link for the hypothesis 
of Langner (1992) that pitch is extracted by periodicity analysis in the 
midbrain and then coded, and transmitted up to the cortex, as part of the 
low-frequency section of the auditory neural pathway. While the exact 
location of the now discovered pitch neurons in the cortex remains to be 
determined by future anatomical studies, the new physiological data indicate 
that they may not only be present in the low-frequency section of the 
primary auditory cortex, but also in adjacent low-frequency sections of 
secondary auditory fields. Such a distribution would agree with the 
important role of pitch in the high-order processes that underlie sound 
identification and acoustic communication.

An interesting detail of the new results is the following one: When partials 
6 and 7 of the complex tone stimulus were the two lowest ones, pitch 
salience, as measured in neuronal firing rate, was still optimum. But when 
partials 7 and 8 were the two lowest ones, pitch salience was clearly 
sub-optimum (Fig. 4c). This breakpoint in pitch salience above partial 7 
agrees exactly with psychoacoustic data from humans for the pitch range of 
the central octave of music (C4-C5). This finding adds to previous data 
suggesting that the origin of the breakpoint lies in the laminar 
architecture of the auditory midbrain (Braun, 1999). Because the cochlea is 
smaller in marmosets than in humans, frequency resolution at this level is 
likely to be better in humans. But frequency resolution at the midbrain 
level, which apparently determines the contribution of partials in pitch 
detection (Braun, 1999), may be very similar in both species.

Bendor, D., Wang, X. (2005). The neuronal representation of pitch in primate 
auditory cortex. Nature, 436, 1161-1165.

Biebel, U.W., Langner, G. (1997). Evidence for "pitch neurons" in the 
auditory midbrain of chinchillas. In: Syka, J. (Ed.), Acoustic Signal 
Processing in the Central Auditory System. Plenum Press, New York, pp. 
263-269.

Biebel, U.W., Langner, G. (2002). Evidence for interactions across frequency 
channels in the inferior colliculus of awake chinchilla. Hear. Res. 169, 
151-168.

Braun, M., (1999). Auditory midbrain laminar structure appears adapted to f0 
extraction: further evidence and implications of the double critical 
bandwidth. Hear. Res. 129, 71-82.

Braun, M., (2000). Inferior colliculus as candidate for pitch extraction: 
multiple support from statistics of bilateral spontaneous otoacoustic 
emissions. Hear. Res. 145, 130-140.

Langner, G., (1992). Periodicity coding in the auditory system. Hear. Res. 
60, 115-142.

Langner, G., Schreiner, C.E., Biebel, U.W., (1998). Functional implications 
of frequency and periodicity coding in auditory midbrain. In: Palmer, A.R., 
Rees, A., Summerfield, A.Q., Meddis, R. (Eds.), Psychophysical and 
Physiological Advances in Hearing. Whurr, London, pp. 277-285.

Rees, A. and Sarbaz, A. (1997) The influence of intrinsic oscillations on 
the encoding of amplitude modulation by neurons in the inferior colliculus. 
In: J. Syka (Ed.), Acoustic Signal Processing in the Central Auditory 
System, Plenum Press, New York, pp. 239-252.

Schreiner, C.E., Langner, G., (1997). Laminar fine structure of frequency 
organization in auditory midbrain. Nature 388, 383-386.


Martin

----------------------------

Martin Braun
Neuroscience of Music
S-671 95 Klässbol
Sweden
web site: http://w1.570.telia.com/~u57011259/index.htm