Changes in cat primary auditory cortex after minor-to-moderate pure-tone induced XXXX .

@entity468 @entity1577 @entity130 @entity393
In this paper we present findings in the primary auditory cortex of @entity468 exposed for 2 h to a 115 dB SPL, 6 kHz tone at 36 days, 56 days or 118 days after birth. We evaluate the effects of age at exposure, amount of @entity393 , and time after induction of @entity130 on the functional reorganization of the cortical tonotopic map. We found a fairly sharp demarcation in the amount of @entity393 (20-25 dB) that caused cortical reorganization. For localized hearing losses, unmasking of excitatory contributions of neighboring frequency regions was found. For @entity468 showing reorganization of the tonotopic map, the frequency-tuning curve bandwidth at 20 dB above threshold at @entity1577 (BW(20dB)) increased with increasing threshold at @entity1577 . Threshold at @entity1577 , and BW(20dB) increased with time after exposure. Minimum spike latency was initially increased, but subsequently decreased with time after exposure at a rate that was two times faster in @entity468 with reorganized cortex than in @entity468 with normal tonotopic maps, to reach the same asymptotic value. Thresholds at @entity1577 were correlated with the peripheral @entity393 at near @entity1577 frequencies as estimated from ABR measurements. The correlation between BW(20dB) and @entity1577 threshold suggests that part of the reorganization could be due to 'residual' sensitivity of the high frequency neurons to not-affected lower or higher frequencies. However, for CFs above 6 kHz, the BW(20dB) for @entity468 with reorganization of the tonotopic map was significantly lower (on average 0.3 octave, P<0.05) than for @entity468 with normal tonotopic maps. This is not what one would expect in cases of pseudo-plasticity characterized by concurrent shifts in BW(20dB) and @entity1577 as a result of residual sensitivity to lower frequencies.
