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Abstract
Changes in spontaneous activity, recorded over 15-min periods before, immediately
after and within hours after an acute acoustic trauma, were studied in primary auditory
cortex of ketamine-anesthetized cats. We focused on the spontaneous firing rate (SFR),
the peak cross-correlation coefficient (rho) and burst-firing activity. Multi-units
(MUs) were grouped according to characteristic frequency (CF): MUs with a CF below
the trauma-tone frequency (TF) were labeled as Be, those with a CF within 1 octave
above the TF were labeled as Ab1 and those with a CF more than 1 octave above the
TF were labeled as Ab2. Immediately after the trauma, the SFR was not significantly
changed. The percentage of time that neurons were bursting, the mean burst duration,
the number of spikes per burst and the mean inter-spike interval in a burst were enhanced.
rho was locally increased in the Ab1-Ab2 and Ab2-Ab2 groups. A few hours post trauma,
the SFR was increased in the Be and Ab2 groups, whereas burst-firing returned to pre-exposure
levels. Moreover, rho was elevated in the Be-Ab2, Ab1-Ab2 and Ab2-Ab2 groups; this
increase was significantly correlated to the changes in SFR. The results are discussed
in the context of a neural correlate of tinnitus.