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Re: Rationale for Critical Bands
Dick and Alain wondered if the following two bodies of evidence were likely
to be related.
1) Spectral band filters, as observed in psychoacoustics and in behavioral
experiments, are sliding spectral windows. A catalogue of fixed borders
between filter bands along the frequency scale have never been found.
2) The central nucleus of the inferior colliculus (ICC) in the mammalian
auditory midbrain is organized in stacked laminae that represent frequency
bands approximately corresponding to the behavioral band filters. The lamina
edges constitute an catalogue of fixed frequencies.
The answer is that the two bodies of evidence appear to be related when one
considers the neural connectivity within and across the laminae.
Neural connectivity for band filtering:
The general mechanisms here are neuron-centered bands of lateral inhibition
and lateral facilitation. These mechanisms can be anatomically realized
independent from the shape of neuron arrays. Linear arrays, as in the
cochlea, or arrays in stacked laminae, as in midbrain and thalamus, are both
possible solution for neuron-centered bands of lateral inhibition and
Band filtering in stacked laminae:
Neuron arrays in stacked laminae provide the advantages of space economy and
connectivity economy. A typical observation in ICC physiology is lateral
inhibition within a frequency range of a lamina (reviewed in Braun, 1999).
The underlying neural connectivity can be organized most economically by
spreading out a neuron-centered inhibitory network (a) within the neuron's
own lamina and (b) toward the near-side halves (frequency-wise) of the two
adjacent laminae. The necessary within-lamina and oblique-across-laminae
fiber networks of inhibitory GABA neurons has indeed been established in
extensive anatomical studies of this nucleus (same ref.). The principles of
connectivity economy for beyond-lamina-space lateral facilitation have also
been shown in anatomical studies (same ref.).
In summary, if one wants to understand how band filtering is realized in the
mammalian ICC, it is not enough to read the physiological reports on neuron
recordings. It is also necessary to read the anatomical reports on neuron
Neuroscience of Music
S-671 95 Klässbol
----- Original Message -----
From: "Alain de Cheveigne'" <Alain.de.Cheveigne@xxxxxx>
Sent: Monday, June 28, 2010 6:13 PM
Subject: Re: Rationale for Critical Bands
Malmierca et al's paper shows a discontinuous