Development of hyperactivity after acoustic trauma in the guinea pig inferior colliculus

The time of onset of hyperactivity (increased spontaneous firing rates) was investigated by single neuron recording in the inferior colliculus (IC) of guinea pigs subjected to unilateral acoustic trauma (exposure to a loud 10 kHz tone). Hyperactivity was present by 12 h post acoustic trauma whereas data obtained within approximately 4 h of the cessation of acoustic trauma found no evidence of hyperactivity. These data suggest that hyperactivity in the IC begins at some time between 4 and 12 h post trauma and is a relatively rapid plastic event beginning within hours rather than days post cochlear trauma. This is consistent with results reported in the cat auditory cortex (Norena and Eggermont, 2003). Hyperactivity did not show any further systematic increase between 12 h and up to 2 weeks post acoustic trauma. At recovery times of 12 and 24 h hyperactivity was widespread across most regions of the IC but at longer recovery times, it became progressively more restricted to ventral regions corresponding to the regions of the cochlea where there was persistent damage.