The Journal of Neuroscience, 2001, 21:RC147:1-5
RAPID COMMUNICATION
Oscillation May Play a Role in Time Domain Central Auditory
Processing
Alexander V.
Galazyuk and
Albert S.
Feng
Department of Molecular and Integrative Physiology, and the Beckman
Institute, University of Illinois, Urbana, Illinois
61801
To study how sound intensity altered the temporal response pattern
of a unit, we recorded from 92 single neurons in the inferior colliculus (IC) of the little brown bat and investigated their firing
patterns in response to brief tone pulses (2 msec duration) at the
characteristic frequency of the unit over a wide dynamic range (10-90
dB sound pressure level). We found two unusual response characteristics at high sound levels in approximately one-third of the
IC neurons investigated. For 16 IC neurons (17%), an increase in sound
level not only elicited a shorter response latency and an increase in
spike count but also transformed the firing pattern of the unit from
phasic to periodic; this pattern was more pronounced at higher sound
levels. The firing periodicity was unit specific, ranging from
1.3 to 6.7 msec. Twenty-seven IC neurons (29%) exhibited a
longer response latency at higher sound levels compared with lower sound levels [i.e., paradoxical latency shift (PLS)]. The majority of this population showed a one or more quantum increase in
latency when sound level was elevated. The quantum shift was also unit
specific, ranging from 1.2 to 8.2 msec. We further investigated the
firing patterns of 14 IC neurons showing PLS before, during, and after
iontophoretic application of bicuculline. For 12 of these neurons, drug
application abolished the PLS and transformed the firing patterns of
the unit at high sound levels from phasic into sustained periodic
discharges. Our results suggest that neural oscillation in combination
with ordinary inhibition may be responsible for the creation of PLSs
shown previously to be important for temporal information processing.
Key words:
paradoxical latency shift; inferior colliculus; bat; echolocation; delay-tuned response; hearing; temporal processing
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