Symposium: Deviance detection along the auditory pathway
Friday, Sep 11, 2015
Cortical mapping of mismatch negativity in rat
Research Center for Advanced Science and Technology, the University of Tokyo, Tokyo, Japan
In animal studies, the existence of the homolog MMN to human has been debated because, in some recent studies, MMN-like responses were best explained by stimulus-specific adaptation (SSA). In this study, we aimed to investigate whether the putative MMN (MMNp) in rats is a mere effect of SSA or has comparable properties to human MMN. A surface microelectrode array recorded auditory evoked potential (AEP) epipially from rat auditory cortex under anesthesia, while the stimuli were presented in an oddball manner. In both of the standard and deviant AEP, middle-latency positive potential (P1) was recorded. By contrast, only in the deviant AEP, MMNp was recorded as a negative deflection. We found that this MMNp and P1 were functionally different in the following four ways. First, while P1 exhibited strong SSA, MMNp didn’t appear in “many standard” control, suggesting that MMNp isn’t a mere effect of SSA. Second, the spatial distribution of P1 and MMNp was different: P1 mainly elicited from the core region of the auditory cortex, however, MMNp spread toward the belt region in addition to the core region. Third, blockage of the NMDA receptors extinguished MMNp, but didn’t affect P1. Fourth, trial-to-trial variation of P1 amplitude showed a unimodal distribution, while MMNp amplitude showed a bimodal distribution, suggesting that, while SSA is always observed at every deviant, MMNp is generated only in some trials. Thus, the MMNp in rat is likely functionally different from P1 with SSA, and in turn, may be comparable to human MMN.