The mismatch negativity (MMN) is a component of the auditory event-related brain potential which is elicited by the infrequent stimuli within the repeated frequent stimuli. The stimulus sequence which generates the MMN has the property which elicit following two automatic processes: (1) the neural model for frequent stimulus is established, and difference between incoming stimulus and the model is detected (Cowan, Winkler, Teder, & Naatanen, 1993) and/or (2) the neural model for the context, infrequent as figure and frequent as ground, is established, and the attention to figure is called.
The Papez circuit is known to be critical for memory because the demage of these regions cause the memory deficit. In this study, auditory evoked potentials for frequent and infrequent tones in the above stimulus sequence were recorded from the regions of the Papez circuit (dentate gyrus, mammillary body, anterior thalamus) and cortices (auditory and entorhinal).
The purpose of this study is to examine following three : (1) whether the components which correspond to the automatic processes appear or not in the regions of the Papez circuit; and if these components appear, (2) the temporal relation between the information processing in the Papez circuit and that in cortical area by comparing the latencies of processing in the Papez circuit and that in cortical area by comparing the latencies of components; (3) the effects of stimulus appearance rate on those components in the Papez circuit.
In the regions of the Papez circuit, the amplitudes of the positive component peaking at about 30 and 70msec for infrequent tones were higher than those for frequent tones. But in the cortical area, only the amplitude of positive component peaking at about 70msec for infrequent tones was higher than those for frequent tones. These phenomenon disappeared as frequent and infrequent tones came to be more equal in the stimulus appearance rate. The results suggested that the information processing which based on the neural model of the frequent standard stimulus and/or on the context of global stimulus sequence occurred in the cortical area and the Papez circuit in parallel.