Symposium: Deviance detection along the auditory pathway
Friday, Sep 11, 2015
Stimulus-specific adaptation, repetition suppression, and the MMN: bridging the gap with small-animal MEG
Ear Institute, University College London, London, United Kingdom
In animal models, single-neuron response properties such as stimulus-specific adaptation and repetition suppression have been described as possible precursors to the mismatch negativity. In humans, brain responses to stimulus change are often studied using magnetoencephalography (MEG). We attempted to bridge the gap between the animal and human studies by characterising responses to changes in the frequency of repeated tone series in the anaesthetised guinea pig using the novel technology of non-invasive small-animal MEG. We found that: (1) auditory evoked fields (AEFs) qualitatively similar to those observed in human MEG studies can be detected noninvasively in rodents using small-animal MEG; (2) guinea pig AEF amplitudes reduce rapidly with tone repetition, and this AEF reduction is largely complete by the second tone in a repeated series; and (3) differences between responses to the first (deviant) and later (standard) tones after a frequency transition resemble those previously observed in awake humans using a similar stimulus paradigm. These data raise the possibility that MMN-like latency shifts can arise through differential effects of tone repetition on the latency of early versus late deflections in the tone-evoked brain response. Moreover, the similarities between our results obtained in anaesthetised guinea pigs and previous results obtained in awake humans using a similar stimulus paradigm suggest that MMN-like latency shifts can be generated by low-level adaptive processes independent of conscious awareness.