Interindividual variability in EEG correlates of attention and limits of functional mapping.

In this study, we analyzed the EEG oscillatory activity induced during a simple visual task, in search of spectral correlate(s) of attention. This task has been previously analyzed by conventional event-related potential (ERP) computation, and Slow Potentials (SPs) were seen to be highly variable across subjects in topography and generators [Basile LF, Brunetti EP, Pereira JF Jr, Ballester G, Amaro E Jr, Anghinah R, Ribeiro P, Piedade R, Gattaz WF. (2006) Complex slow potential generators in a simplified attention paradigm. Int J Psychophysiol. 61(2):149-57]. We obtained 124-channel EEG recordings from 12 individuals and computed latency-corrected peak averaging in oscillatory bursts. We used current-density reconstruction to model the generators of attention-related activity that would not be seen in ERPs, which are restricted to stimulus-locked activity. We intended to compare a possibly found spectral correlate of attention, in topographic variability, with stimulus-related activity. The main results were (1) the detection of two bands of attention-induced beta range oscillations (around 25 and 21 Hz), whose scalp topography and current density cortical distribution were complex multi-focal, and highly variable across subjects (topographic dispersion significantly higher than sensory-related visual theta induced band-power), including prefrontal and posterior cortical areas. Most interesting, however, was the observation that (2) the generators of task-induced oscillations are largely the same individual-specific sets of cortical areas active during the pre-stimulus baseline. We concluded that attention-related electrical cortical activity is highly individual-specific, and possibly, to a great extent already established during mere resting wakefulness. We discuss the critical implications of those results, in combination with results from other methods that present individual data, to functional mapping of cortical association areas.