Plasticity of spontaneous neural activity in the dorsal cochlear nucleus after intense sound exposure.

Increases in multiunit spontaneous activity (hyperactivity) can be induced in the dorsal cochlear nucleus (DCN) by intense sound exposure. This hyperactivity has been observed in the hamster and rat following exposure to a 10 kHz tone at a level of 125-130 dB SPL for a period of 4 h. The present study demonstrates that the onset of this hyperactivity is not immediate, but develops in the DCN between 2 and 5 days after exposure. Mean rates of multiunit spontaneous activity increased sharply from below normal levels at day 2 to higher than normal levels at day 5. The mean magnitude of activity continued to increase more gradually over the next 6 months. During this period, changes in the distribution of hyperactivity across the tonotopic array were also noted. The hyperactivity was more broadly distributed across the DCN at the early post-exposure times (5 and 14 days) than at later post-exposure recovery times (30 and 180 days), and peak activity was found at increasingly more medial positions over this time frame. These changes over time indicate that the mechanisms leading to hyperactivity following intense sound exposure are more complex than previously realized.