PB 7 The role of Rolandic alpha-activity on processing of subliminal and supraliminal somatosensory stimulation during selective spatial attention

Abstract

Research questions We investigated, whether attentional modulation of somatosensory evoked potentials (SEPs) are mediated by variations in the rolandic alpha-rhythm. Furthermore, we asked whether the attention effect is limited to consciously perceivable (i.e. supraliminal) stimuli, or also applies to imperceptible (i.e. subliminal) stimulation. Methods To address these questions, we recorded EEG in healthy volunteers (n = 40) undergoing supraliminal and subliminal finger nerve stimulation at the left or right index finger and identified both oscillatory activity and SEPs. Participants performed the following detection task: Spatial attention should be directed either to the left or the right index finger and participants indicated perception of stimuli only at the attended finger. Results Detection rates for supraliminal stimulation was 71%, when attention was on the left and 74%, when it was on the right finger, respectively (detection rates for subliminal stimulation ∼ 0%). In the EEG, selective spatial attention increased SEP-amplitudes (in a time window 50–60 ms after stimulation; P1) both to supraliminal and subliminal stimulation. Mu-rhythm amplitudes directly preceding stimulation showed a negative quadratic relationship to P1-amplitudes under attention, which reversed, when the stimulated finger was not attended. I.e. the same mu-rhythm amplitude was associated with the highest P1-amplitudes during attention and smallest P1-amplitudes during lack of attention. Conclusion The modulation of the mu-rhythm obviously seems to support the behavioral goal: ‘detect’ stimuli at the cued while ‘ignoring’ the other index finger. To summarize, our results show, that – firstly – selective spatial attention enhances central processing of supraliminal as well as subliminal stimulation and – secondly – they underline the importance of mu-rhythm activity in mediating the effect of attention on stimulus processing.