Source localization of α-ERD induced by target stimuli across all sensory modalities.

<p>Talairach coordinates (x, y, z) of the sources of the α-ERD are, -9, -99, -7 mm and 16, -95, -12 mm; -6, -99, -5 mm and 14, -96, -4 mm; -6, -99, -5 mm and 17, -97, -3 mm; and -6, -99, -5 mm and 16, -95, -12 mm for auditory, visual, somatosensory, and pain target conditions respectively. Note that the sources of the α-ERD induced by target stimuli across all sensory modalities are similarly located at the bilateral occipital cortices.</p

Percentage of accuracy to distinguish different tonic stimulation conditions using spectral power with different length of consecutive epochs.

<p>Each dot represents percentage of accuracy to distinguish different stimulation conditions in the corresponding length of consecutive epochs. Red lines represent the results to distinguish four stimulation conditions revealed by 4-level one-way repeated measures ANOVA. Lines in yellow, green, and blue respectively represent the results to distinguish conditions A and D, B and D, as well as C and D, which were revealed by post hoc analysis. The black dashed lines represent the percentage of accuracy at 95%. Spectral power within alpha frequency band (10–15 Hz) at contralateral-central electrodes (C2, C4, CP2, and CP4; left) could be used to distinguish conditions B and D, as well as C and D. Spectral power within gamma frequency band (30–100 Hz) at frontal-central (Fz, FC1, FC2, and Cz; middle) and ipsilateral-central electrodes (C1, C3, CP1, and CP3; right) could be used to distinguish conditions A and D.</p

Relationships between spectral power differences and subjective intensity of pain perception.

<p>Negative correlations between spectral power differences (left panel, D–B, D–C) within alpha frequency band (10–15 Hz) and averaged subjective pain intensity during the interval of 2^nd to 4^th min were maximal at contralateral-central electrodes (C2, C4, CP2, and CP4). Positive correlations between spectral power difference (left panel, D–A) within gamma frequency band (30–100 Hz) and averaged subjective pain intensity during the interval of 2^nd and 4^th min were maximal at prefrontal-central (left: AF3, AF4, F1, Fz, and F2) and ipsilateral-posterior (right: CP1, CP3, CP5, P1, P3, and P5) electrodes. Specifically, the subjective pain intensity at each min were negatively correlated with alpha spectral power difference (D–B, D–C) at contralateral central electrodes (marked in the white circles), and positively correlated with gamma spectral power difference (D–A) at prefrontal-central and ipsilateral-posterior electrodes (marked in white circles). Each dot represents values from each subject, and black lines represent the best linear fit.</p

Experimental design and behavioral results.

<p>Top panel: The experiment consisted of four stimulation conditions (A: resting condition; B: innoxious-distracted condition; C: noxious-distracted condition; D: noxious-attended condition), which were presented in counterbalanced order within a single session. Each stimulation condition last for 5 minutes with a 10-minute break between consecutive stimulation conditions. Bottom panel: In condition D, the reported NRS scores at the end of each minute were compared to assess the possible change of pain perception with the prolonged duration of noxious stimulation. Error bars represent, for each minute, ± SD across subjects. Asterisk (*) indicates a significant difference (P<0.05, Tukey’s post hoc tests).</p

Source localizations of P300 elicited by target stimuli across all sensory modalities.

<p>Distributed sources estimated around P300 peak latencies using CLARA are superimposed on standard MR image template, and the color is coded according to their intensity, expressed in nAm/cm³. Talairach coordinates (x, y, z) of the sources of P300 are -9, -41, 37 mm; -9, -47, 19 mm; -9, -41, 13 mm; and -9, -47, 25 mm for auditory, visual, somatosensory, and pain target conditions respectively. Note that the sources of the P300 elicited by target stimuli across all sensory modalities are similarly located at the posterior cingulate cortex.</p

Comparison of normalized power spectra among four stimulation conditions.

<p>Normalized power spectra, measured at contralateral-central electrodes (C2, C4, CP2, and CP4; top), frontal-central electrodes (Fz, FC1, FC2, and Cz; middle), and ipsilateral-central electrodes (C1, C3, CP1, and CP3; bottom), were respectively displayed in yellow, green, blue, and red for conditions A, B, C, and D. As marked in grey, significant differences of power spectra across stimulation conditions were dominantly observed at contralateral-central electrodes from 10 to 15 Hz (top), at frontal-central electrodes from 30 to 55 Hz and from 60 to 100 Hz (middle), and at ipsilateral-central electrodes from 30 to 100 Hz (bottom). The summarized spectral power, measured at contralateral-central electrodes (top) within alpha band (10–15 Hz, top), at frontal-central (middle) and ipsilateral-central (bottom) electrodes within gamma band (30–100 Hz), were respectively marked in yellow, green, blue, and red, and were compared among four stimulation conditions. Error bars represent, for each condition, ± SEM across subjects. Asterisk * indicates a significant difference (P<0.05, Tukey’s post hoc tests).</p

Time-varying normalized power spectra among four stimulation conditions.

<p>Grand averaged time frequency distributions of the spectral power density difference (left panel, D–B, D–C) were measured on contralateral central electrodes (C2, C4, CP2, and CP4), and power differences (right panel, D–A) were measured at frontal central (Fz, FC1, FC2, and Cz) and ipsilateral central (C1, C3, CP1, and CP3) electrodes. The dashed lines represent the start of each min, and the alpha suppression and gamma enhancement were marked in white rectangle on the time-frequency distribution of spectral power difference. Grand averaged time-varying spectral power curve at contralateral central electrodes within alpha (10–15 Hz) frequency band (left panel), and at frontal and ipsilateral central electrodes (right panel) within gamma (30–100 Hz) frequency band were also displayed in yellow, green, blue, and red for conditions A, B, C, and D. The intervals with significance difference across the conditions were marked in grey.</p

Reaction time, P300 latency and amplitude, α-ERD magnitude in the target condition, and P200 latency and amplitude, α-ERD magnitude in the non-target condition.

<p>Reaction time, P300 latency and amplitude, α-ERD magnitude in the target condition, and P200 latency and amplitude, α-ERD magnitude in the non-target condition.</p

Grand average ERPs and scalp topographies of P200 and P300 for all sensory modalities in target and non-target conditions.

<p>Grand average ERP waveforms are measured at Pz in the target condition, and at Cz in the non-target condition across all sensory modalities. X-axis, latency (ms); Y-axis, amplitude (µV). Grand average ERP waveforms evoked by auditory, visual, somatosensory, and pain stimuli are presented in orange, yellow, green, and blue respectively. Noteworthy is that the scalp topographies of P300 elicited by the target stimuli across all sensory modalities were remarkably similar, and displayed a clear maximum at the parietal electrodes (around Pz). The scalp topographies of P200 elicited by the non-target stimuli across all sensory modalities were also remarkably similar, and displayed a clear maximum at the central electrodes (around Cz).</p

Grand average TFDs and α-ERD scalp topographies for all sensory modalities in target and non-target conditions.

<p>In the target condition, grand average TFDs are measured at (P3+P4+P5+P6+PO3+PO4)/6 for all sensory modalities, while, in the non-target condition, grand average TFDs are measured at (PO3+PO4+PO7+PO8+O1+O2)/6 for auditory and visual modalities and at (C4+C6+CP4)/3 for somatosensory and pain modalities. X-axis, latency (ms); Y-axis, frequency (Hz). Color scale represents baseline corrected oscillatory magnitude (ER%). It should be noted that the α-ERD induced by target stimuli is significantly larger in intensity, greater in size, and later in latency than that induced by non-target stimuli. The scalp topographies for “top 20%” magnitudes of α-ERD within the predefined ROI (marked using white rectangles) displayed a clear maximum at occipital regions across all sensory modalities in the target conditions, while, in the non-target conditions, they showed a clear maximum at occipital regions for auditory and visual modalities, and at contralateral central regions for somatosensory and pain modalities.</p