The processing of information from the sensory (eg. eye) up to the brain (primary area) is well established now. However, the relationship from the primary level in the brain to the more higher functions, which give access to conscious perception still needs to be explored.
To study this relationship, we used a Local-Global paradigm (1). The local effect (LE) is related to the mismatch negativity (MMN), while the global effect (GE) reveals the P300. In this experiment, we are interested in the neuronal relationship between the local and global effect, ie. the local by global (LxG) interaction. To study these effects, an EEG source reconstruction was performed using SPM12, with a Multiple Sparse Priors inverse model. A baseline (400 - 600ms) was applied before the onset of the stimulus. The source inversion ran from 400ms to the end of the epoch. We analyzed the sources for these effects in three different windows: MMN (700 750 ms)(2), P3a (850 950ms) and P3b (1000 1200ms)(3). An ANOVA was used to find the significant clusters: cluster forming threshold is set at 0.001, and Family-Wise Error (FWE) rate correction at 0.05. We also illustrated how the amplitude at the sources evolves by plotting the time series generated at the source level.
The MMN window shows an LE in the temporal lobe source. The P3 effect shows a strong GE covering frontal, temporal and parietal areas. The P3a window presents an LE in temporal, and a GE in temporal and frontal. In the P3a window, we found a LxG interaction in the temporal area. The sources related to the MMN and the P300 are consistent with the literature. The interaction in the P3a window, significant in the temporal area, reveals an interaction between the MMN and P300 effects. This suggests a more complex hierarchy of processing than previously reported, which will be discussed with regard to the global workspace theory of conscious experience (4).
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