5 Hz). Total power was computed relative to a baseline interval (−1.6 to −1.2 s before electrical stimulus onset). Average power in the baseline interval was first subtracted from the interval after clip onset and before electrical stimulus onset (prestimulus interval; −1 to 0 s) and the resulting difference was divided by the baseline interval activity as follows: Pow(t, f )normalised = 100 * ((Pow(t, f )prestimulus − Pow( f )baseline)/Pow( f )baseline) (e.g. Pfurtscheller & Aranibar, 1977). For the statistical analysis, a cluster-based permutation test was applied on electrode–time–frequency
data (Maris & Oostenveld, 2007; Schneider et al., 2011). The dependent samples t-tests were thresholded at P = 0.005 and the permutation P-value of the cluster was set to P = 0.05. For the source reconstruction, a linear beamforming approach was applied (dynamic imaging of coherent sources; Van Veen et al., 1997; Gross
et al., 2001). In this approach, APO866 purchase source-level power is calculated using an adaptive spatial filter that passes activity from one specific location of interest with unit gain and maximally suppresses activity from surrounding locations. In the present study, one common filter was used, comprising all conditions (i.e. needle and Q-tip) as well as all time intervals (i.e. baseline and prestimulus). As linear beamforming is based on the calculation of the cross-spectral density matrix over trials, this approach is particularly suitable for the analysis of total power in the human electroencephalogram (Schneider
et al., 2008, 2011). The leadfield selleck screening library matrix was calculated on a boundary element model for each grid point in the brain with a regular 7 mm grid using a forward model based on closed compartments representing brain tissue (gray and white matter), bone, and skin (Oostenveld et al., 2001). A spatial filter was constructed for each grid point and subsequently applied to estimate the power at that source location. In accordance with previous studies on pain anticipation (Babiloni et al., 2005a, 2006) and with the activity patterns observed in the present study, the main focus of the statistical analysis of oscillatory responses was on the examination of ABA (8–12 Hz). The time interval for the source analysis was selected based Linifanib (ABT-869) on the results of the cluster-based permutation test on electrode–time–frequency data (Fig. 3) and was centered at −0.5 s (interval −0.7 to −0.3 s) before electrical stimulus onset; the respective baseline was centered at −1.4 s (interval −1.6 to −1.2 s). Source data were analysed voxel-wise by means of a cluster-based permutation test. The dependent samples t-tests for this analysis were thresholded at P = 0.0001 and the permutation P-value of the cluster was set to P = 0.05. Based on the results obtained in the cluster-based analysis of source data (Fig. 5), a region in the posterior cingulate cortex (PCC) and in the right fusiform gyrus (FG) was selected for further analysis.