The Journal of Neurophysiology Vol. 82 No. 5 November 1999, pp. 2358-2371
Copyright ©1999 by the American Physiological Society
1Center for Neuroscience and Section of
Neurobiology Physiology and Behavior,
Sutter, M. L.,
C. E. Schreiner,
M. McLean,
K. N. O'connor, and
W. C. Loftus.
Organization of Inhibitory Frequency Receptive Fields in Cat
Primary Auditory Cortex. J. Neurophysiol. 82: 2358-2371, 1999. Based on properties of excitatory frequency
(spectral) receptive fields (esRFs), previous studies have indicated
that cat primary auditory cortex (A1) is composed of functionally
distinct dorsal and ventral subdivisions. Dorsal A1 (A1d) has been
suggested to be involved in analyzing complex spectral patterns,
whereas ventral A1 (A1v) appears better suited for analyzing narrowband sounds. However, these studies were based on single-tone stimuli and
did not consider how neuronal responses to tones are modulated when the
tones are part of a more complex acoustic environment. In the visual
and peripheral auditory systems, stimulus components outside of the
esRF can exert strong modulatory effects on responses. We investigated
the organization of inhibitory frequency regions outside of the
pure-tone esRF in single neurons in cat A1. We found a high incidence
of inhibitory response areas (in 95% of sampled neurons) and a wide
variety in the structure of inhibitory bands ranging from a single band
to more than four distinct inhibitory regions. Unlike the auditory
nerve where most fibers possess two surrounding "lateral"
suppression bands, only 38% of A1 cells had this simple structure. The
word lateral is defined in this sense to be inhibition or suppression
that extends beyond the low- and high-frequency borders of the esRF.
Regional differences in the distribution of inhibitory RF structure
across A1 were evident. In A1d, only 16% of the cells had simple
two-banded lateral RF organization, whereas 50% of A1v cells had this
organization. This nonhomogeneous topographic distribution of
inhibitory properties is consistent with the hypothesis that A1 is
composed of at least two functionally distinct subdivisions that may be
part of different auditory cortical processing streams.