Moderate noise trauma in juvenile cats results in profound cortical topographic map changes in adulthood

Cortical topographic map changes have been reported after profound drug-ind uced hearing loss in neonates, after progressive high-frequency hearing los s, and after mechanically induced lesions in the cochlea of adult animals. The present study demonstrates that exposure of 5-week-old kittens to a lou d 6 kHz tone, producing mild to moderate high-frequency hearing loss, induc es a profound reorganization of the frequency map in auditory cortex. In th e reorganized cortical region, the frequency-tuning curves were of normal s harpness with near normal thresholds. Inhibitory tuning curve bandwidths we re similar to those in control animals. Spontaneous activity in the reorgan ized part of the cortex was significantly increased. In contrast, the stren gth of the crosscorrelation of the spontaneous activity of units recorded o n different electrodes was the same in the normal and reorganized part. Min imum first-spike latency was significantly increased in trauma cats, largel y for units at the dorsal side of the sampled region. Because most other ne ural response properties are normal in the reorganized part of cortex, sub- cortical topographic mag changes are likely involved in producing the alter ed cortical topographic maps. (C) 2000 Elsevier Science B.V. All rights res erved.