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 hypera ctivity has been observed in the hamster and rat following exposure to a 10 kHz tone at a level of 115-130 dB SPL for a period of 4 h. The present stu dy 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 mult iunit spontaneous activity increased sharply from below normal levels at da y 2 to higher than normal levels at day 5. The mean magnitude of activity c ontinued to increase mere gradually over the next 6 months. During this per iod, changes in the distribution of hyperactivity across the tonotopic arra y were also noted. The hyperactivity was more broadly distributed across th e DCN at the early post-exposure times (5 and 14 days) than at later post-e xposure recovery times (30 and 180 days), and peak activity was found at in creasingly more medial positions over this rime frame. These changes over t ime indicate that the mechanisms leading to hyperactivity following intense sound exposure are more complex than previously realized. (C) 2000 Elsevie r Science B.V. All rights reserved.