Stimulus-specific adaptation and its dynamics in the inferior colliculus of rat.

Stimulus specific adaptation (SSA) is known as a decrease of neuronal response to stimuli that are commonly presented than those rarely occurred. Previous studies have shown that SSA occurs at different levels of auditory pathway, from inferior colliculus (IC), auditory thalamus to auditory cortex (AC). In this study, we further investigated the properties of SSA in rat IC using oddball paradigm. We found that SSA existed even at a lower repetition rate (1 Hz), besides at relatively higher rates (≥2 Hz) shown in previous studies. We also analyzed the temporal dynamics of adaptation to the entire stimulus sequence. Global and local components were found in the response process. These components include a long-term adaptation during the entire oddball sequence, a short-term increase of responses to common stimuli after rare ones and the effects of stimulus history on current response. By fitting a linear model regarding stimulus local history and global probability, we found both of them affect IC neuronal responses. Our study further supports the existence of SSA in IC and provides detailed properties of the neural processing of novelty detection at midbrain level.