Subject: Re: Rationale for Critical Bands From: Martin Braun <nombraun@xxxxxxxx> Date: Tue, 29 Jun 2010 14:25:07 +0200 List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>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 lateral facilitation. 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 connectivity. Braun (1999): http://www.ncbi.nlm.nih.gov/pubmed/10190753 Martin --------------------------------------------------------------------- Martin Braun Neuroscience of Music S-671 95 Klässbol Sweden ----- Original Message ----- From: "Alain de Cheveigne'" <Alain.de.Cheveigne@xxxxxxxx> To: <AUDITORY@xxxxxxxx> Sent: Monday, June 28, 2010 6:13 PM Subject: Re: Rationale for Critical Bands Malmierca et al's paper shows a discontinuous