Stimulus-specific adaptation in the anesthetized mouse revealed by brainstem auditory evoked potentials

Neural responses to sensory inputs in a complex and natural environment must be weighted according to their relevance. To do so, the brain needs to be able to deal with sudden stimulus fluctuations in an ever-changing acoustic environment. Stimulus-specific adaptation (SSA) is a phenomenon of some neurons along the auditory pathway that show a reduced response to repetitive sounds while responsive to those that occur rarely. SSA has been shown from the inferior colliculus to auditory cortex, but has not been detected in the cochlear nucleus. To discover where SSA is first generated along the auditory pathway, auditory brainstem responses (ABRs) to pure tones were evaluated in anesthetized mice using an oddball paradigm. Using a typical narrow band-pass filter, changes in the ABRs suggest unspecific short-term adaptation may occur as early as the auditory nerve fibers. Furthermore, after applying a wide band-pass filter -allowing the visualization of a late slow wave in the ABR- we found a reduction of the amplitude of the response to repetitive sounds, compared to rare ones, in the slow wave component P0 that follow the fast wave V. Previous studies have shown the P0 shows temporal correlation with the sustained responses of inferior colliculus, thus we suggest that this nucleus is the first to show stimulus specific adaptation in the auditory pathway.