More evidence for a long-latency mismatch response in urethane-anaesthetised mice.

Long-latency mismatch responses to oddball stimuli have recently been observed from anaesthetised rodents. This electrophysiological activity is viewed through 200 to 700 ms post-stimulus; a window that is typically obstructed from analysis by the response to subsequent stimuli in the auditory paradigm. A novel difference waveform computation using two adjoining evoked responses has enabled visualisation of this activity over a longer window than previously available. In the present study, this technique was retroactively applied to data from 13 urethane-anaesthetised mice. Oddball paradigm waveforms were compared with those of a many-standards control sequence, confirming that oddball stimuli evoked long-latency potentials that did not arise from standard or control stimuli. Statistical tests were performed to identify regions of significant difference. Oddball-induced mismatch responses were found to display significantly greater long-latency potentials than identical stimuli presented in an equal-probability context. As such, it may be concluded that long-latency potentials were evoked by the oddball condition. How this feature of the anaesthetised rodent mismatch response relates to human mismatch negativity is unclear, although it may be tentatively linked to the human P3a component, which emerges downstream from mismatch negativity under certain conditions. These results demonstrate that the time dynamics of mismatch responses from anaesthetised rodents are more extensive than previously considered.