Representation of Amplitude Modulated Sounds in Two Fields in Auditory Cortex of the Cat

  • Jos J. Eggermont


Temporally structured sounds such as sine or square-wave modulated carriers and periodic click trains are represented somewhat differently in separate cortical fields in cat (Schreiner and Urbas, 1988) but less so in squirrel monkey (Bieser and Müller-Preuss, 1996). Representation of these complex sounds in cortex has been observed as a modu- lated-rate (AM) wide-band noise (Eggermont, 1993). The average higher BMF in AAF appeared largely due to values obtained in units with CFs above 10 kHz, for lower CFs all BMFs were below 20 Hz. In awake squirrel monkeys Bieser and Müller-Preuss (1996) found a broad range of BMFs from 2 — 128 Hz with a sharp reduction in the number of units with BMFs above 16 Hz. Low modulation frequencies (2 - 64 Hz) were mostly encoded by phase-locked neural responses and higher AM (128 - 512 Hz) sounds showed a distinction in overall-spike-rate variations. A similar view is offered by the recordings of Steinschneider et al. (1980, 1982) in auditory cortex of awake macaques: they found phase-locked activity in the depth-recorded local field potentials up to 250 Hz and for multi-unit activity up to 100 Hz. Because AI and AAF receive similar anatomical projections from the medial geniculate body (MGB; Rouiller et al., 1991) one expects the reason for these apparent differences in the two primary fields of the cat to reside in intrinsic cell properties or in intra-cortical network properties.


Firing Rate Auditory Cortex Inferior Colliculus Rate Code Primary Auditory Cortex 
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© Springer Science+Business Media New York 1997

Authors and Affiliations

  • Jos J. Eggermont
    • 1
  1. 1.Department of PsychologyThe University of CalgaryCalgaryCanada

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