Relation between P300 and event-related theta-band synchronization: a single-trial analysis

Recent reports show that theta-band (4-7 Hz) power is enhanced by target detection in the standard oddball paradigm, which, together with increased P300, is considered as providing complementary neural mechanisms supporting memory and attention processes. We hypothesize that the increased theta event-related synchronization (ERS) may stem largely from not accounting for the trial-to-trial variability of the P300 evoked component and may not reflect a separate mechanism for target detection and related cognitive processing.

EEG was recorded from healthy volunteers performing visual and auditory odd-ball tasks. Ongoing-activity was obtained using two methods: (a) subtracting the ASEO-estimated (analysis of single-trial event-related potentials and ongoing-activity) single-trial ERP from corresponding single-trial EEG time series and (b) subtracting the average event-related potential (AERP) from single-trial EEG time series. Event-related oscillatory activities obtained from the two methods were compared.

The amount of power increase in the theta-band was greatly attenuated for the single-trial based method relative to the traditional AERP method.

Our results suggest that the theta-ERS arises largely from not modeling the trial-to-trial variability of the P300.

ERP components such as the P300 vary from trial-to-trial in both amplitude and latency. The traditional AERP method leaves traces of evoked responses in the residual data which can negatively impact the inference of ongoing oscillatory dynamics. Thus, caution should be exercised in interpreting such phenomena in basic and clinical contexts.