P 186. Inter-and intra-individual differences in the attentional modulation of the somatosensory steady state signal

Introduction In electroencephalography (EEG) research, frequency-tagging has become an important measure for investigating sustained attention in the field of vision, audition and both (cf. Keitel et al., 2011; Saupe et al., 2009; Muller et al., 2003). Frequency-tagged stimuli elicit the steady state evoked potential (SSEP), which is an oscillatory brain response of the same frequency as the driving frequency. Crucially, paying attention to such a stimulus causes an increase in SSEP amplitude compared to when the respective stimulus had to be ignored. In the somatosensory domain however, attentional modulation of the steady state signal seems to be highly variable across and within subjects; i.e. there is either an increased or decreased amplitude when attention is paid to a vibrotactile stimulus. Interestingly, despite this opposing pattern behavioral performance showed that participants seemed to perform the task correctly. The present study wanted to shed light on possible factors causing these inter-and intra-individual differences. Methods and hypotheses We conducted a simultaneous EEG and functional magnetic resonance imaging (fMRI) study because both methods provide us with different markers of attention and brain states at different time scales. We expected to find a direct relationship between the attentional modulation seen in the EEG and fMRI signal. Participants with an increased amplitude of the EEG steady state signal should show an increased BOLD response in primary somatosensory cortex compared to participants with a decreased amplitude. Besides differences in pre-stimulus EEG oscillations (e.g. μ-alpha or μ-beta) and resting state fMRI measures might account for inter and intra-individual alterations in attention effects. Conclusion The present study allows the direct comparisons of EEG, fMRI and behavioral attention markers and thereby paves the road for multi-method approaches in sustained somatosensory attention research.