Inter-study and inter-Individual Consistency and Variability of EEG/ERP Microstate Sequences in Referential Word Production.

Periods of stable global electric field at scalp unfolding during a cognitive task can be linked to brain processes and are therefore well suited to investigate simultaneously qualitative and quantitative differences across conditions or populations of interest. The electrophysiological event-related (ERP) spatio-temporal dynamic has been repetitively investigated in referential word production, but the different designs, settings and analyses do not allow to conclude on the reliability of the microstate sequences across studies and individuals. Here the inter-studies and inter-individual consistency of sequences of scalp topographies were analysed in the ERP data of 118 individuals from five different oral picture naming studies. Averaging the individual ERP data across studies or across random groups yielded the same sequences of microstates, except in two periods of low topographic consistency (in the first 75 ms following picture presentation-C1 VEP component-and in the N170 time-window). In the other time-periods highly consistent patterns of 5 distinct microstates appeared up to 100 ms before the vocal response across studies and individuals. This same sequence of dominant scalp maps also explained a similar proportion of variance in a new dataset of 19 individual ERPs. The observed consistency of microstate sequences across picture naming studies constitutes the premise for the interpretation of the periods of quasi-stable global scalp potentials in terms of mental processes in referential word production but also for the study of deviant neurophysiological patterns in language impaired populations.