Discussion : current EEG state impacts ERP components and behaviour

This symposium explores some aspects of the linkages between the individual's brain state at stimulus onset, ERPs, and associated behavioural outcomes. Along the way, the four papers provide interesting information about current brain state, which may well impact on how we investigate human behaviour in the future. In the first paper, Barry and colleagues report on the importance of the phase of EEG activity at stimulus onset in determining perceptual and cognitive processing. These findings potentially extend the phase-resetting model of ERP genesis. The focus shifts from phase to prestimulus amplitude in the subsequent papers. Age differences in brain dynamics are explored in the second paper, by De Blasio et al. Interestingly, although EEG and ERPs both change with normal ageing, some of the dynamic connections between them remain unchanged, suggesting the entrenched importance of the fundamental mechanisms involved in ERP genesis, while some others possibly reflect positive aspect of neuroplasticity. These findings may provide new insight into normal and pathological ageing. This paper is followed by the report by Karamacoska and colleagues on links between prestimulus EEG amplitudes and response-related outcomes in the Go processing stream of a Go/NoGo task. They found some interesting relationships, particularly involving the delta and theta bands, which affect the ERP analogues of attention, stimulus-related processing, and response efficiency. Certainly, replication of these findings is essential, as there is a growing emphasis being placed on understanding response variability in clinical contexts. The fourth and final paper in this symposium, by Barry et al., investigates how EEG estimates can be improved via frequency-PCA of the EEG spectrum, relative to using the traditional frequency bands. Largely the results confirm previous findings of the direct impact of prestimulus alpha and beta on P3a amplitudes, and the inverse relationship between prestimulus theta and P3b amplitude, and suggest potential research expansions using such data-driven frequency ranges. Overall, the findings from these four papers are very stimulating, and perhaps discussion could focus on the functional importance of these findings to future research in a range of different populations.