The Journal of Neurophysiology Vol. 86 No. 1 July 2001, pp. 475-491
Copyright ©2001 by the American Physiological Society
Spectrotemporal Organization of Excitatory and Inhibitory
Receptive Fields of Cat Posterior Auditory Field Neurons
William C.
Loftus and
Mitchell L.
Sutter
Center for Neuroscience and Section of Neurobiology, Physiology and
Behavior, University of California, Davis, California 95616
Loftus, William C. and
Mitchell L. Sutter.
Spectrotemporal Organization of Excitatory and Inhibitory
Receptive Fields of Cat Posterior Auditory Field Neurons. J. Neurophysiol. 86: 475-491, 2001. The excitatory
and inhibitory frequency/intensity response areas (FRAs) and
spectrotemporal receptive fields (STRFs) of posterior auditory
cortical field (PAF) single neurons were investigated in barbiturate
anesthetized cats. PAF neurons' pure-tone excitatory FRAs
(eFRAs) exhibited a diversity of shapes, including some with very broad
frequency tuning and some with multiple distinct excitatory frequency
ranges (i.e., multipeaked eFRAs). Excitatory FRAs were analyzed after
selectively excluding spikes on the basis of spike response times
relative to stimulus onset. This analysis indicated that spikes with
shorter response times were confined to narrow regions of the eFRAs,
while spikes with longer response times were more broadly distributed
over the eFRA. First-spike latencies in higher threshold response peaks
of multipeaked eFRAs were ~10 ms longer, on average, than latencies
in lower threshold response peaks. STRFs were constructed to examine
the dynamic frequency tuning of neurons. More than half of the neurons
(51%) had STRFs with "sloped" response maxima, indicating that the
excitatory frequency range shifted with time. A population analysis
demonstrated that the median first-spike latency varied systematically
as a function of frequency with a median slope of ~12 ms per octave. Inhibitory frequency response areas were determined by simultaneous two-tone stimulation. As in primary auditory cortex (A1), a diversity of inhibitory band structures was observed. The largest class of
neurons (25%) had an inhibitory band flanking each eFRA edge, i.e.,
one lower and one upper inhibitory band in a "center-surround" organization. However, in comparison to a previous report of inhibitory structure in A1 neurons, PAF exhibited a higher incidence of neurons with more complex inhibitory band structure (for example, >2
inhibitory bands). As was the case with eFRAs, spikes with longer
response times contributed to the complexity of inhibitory FRAs. These data indicate that PAF neurons integrate temporally varying excitatory and inhibitory inputs from a broad spectral extent and, compared with
A1, may be suited to analyzing acoustic signals of greater spectrotemporal complexity than was previously thought.
