More evidence for a long-latency mismatch response in urethane-anaesthetised mice
Prolonged electrophysiological responses to oddball stimuli have recently been observed from anaesthetised rodents. This deviant-related activity is found to extend through 200 to 700 ms post-stimulus; a window typically obstructed from analysis by the response to subsequent stimuli in the auditory sequence. A simple methodological development in terms of difference waveform computation using two adjoining evoked responses has enabled visualisation of this activity over a longer window of analysis than previously available. In the present study, the double-epoch subtraction 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 at every time point from 0 to 700 ms post stimuli to highlight 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 is considered to emerge downstream from mismatch negativity.