Pain-Induced Gamma Oscillations in Somatosensory Cortices

<div><p>(A) Group mean locations of contralateral primary (S1 cl) and bilateral secondary somatosensory (S2 cl and S2 il) cortices. Locations were obtained from analysis of evoked responses to noxious laser stimuli. Individual tomographic maps of pain-evoked power increases were calculated and averaged across subjects, resulting in a group-mean tomographic map of pain-evoked power increases with dimensionless values (see Methods for details). Talairach coordinates of activations were: −20,−37, and 57 (S1 cl), −45,−15, and 22 (S2 cl), and 50,−16, and 19 (S2 il). The additional colored voxels were not consistently found in single participants and have not been included in further analysis.</p> <p>(B) Group-mean TFRs for each of the three areas. The TFRs show power as a function of time and frequency. Power is coded as <i>z</i>-score calculated from a 1,000-ms baseline period. Significance of activations was determined by using permutation statistics; areas below the 95% confidence level are masked by transparent gray shading. Significant oscillations following noxious stimuli (stimulus onset at 0 ms) are evident in contralateral S1 in the high gamma range at a latency of about 200 ms. Please note that the different frequency peaks do not represent harmonics, but result from interindividual variability in frequency of gamma oscillations. No significant oscillations can be seen for bilateral S2 at any time.</p> <p>(C) Group-mean amplitudes of induced gamma oscillations (60–95 Hz, black lines) and evoked activity (gray lines) from contralateral S1 and bilateral S2. The left and right axes and labels correspond to evoked activity and induced gamma oscillations, respectively. Evoked activity is given in source strength and induced gamma oscillations are given in <i>z</i>-scores. Evoked activity and induced gamma oscillations in S1 show the same peak latency (evoked: 190 ± 10 ms; induced gamma: 192 ± 15 ms; mean ± the standard error of the mean [s.e.m]; <i>p</i> > 0.8, two-tailed Wilcoxon signed-rank test).</p></div

Pain Intensity, Amplitudes of Induced Gamma Oscillations, and Amplitudes of Evoked Responses as a Function of Stimulus Intensity

<p>Mean power changes of induced gamma oscillations (black line, left panel) and evoked activity (black line, right panel) at 100–300 ms with respect to baseline were computed for all four stimulus intensities and compared to mean pain ratings (gray lines). Error bars depict ± the standard error of the mean (s.e.m.) Induced gamma oscillations, evoked responses, and pain intensity increase with stimulus intensity. Spearman's correlation coefficient between induced gamma oscillations and pain intensity was 0.96 (<i>p</i> = 0.003), and between evoked responses and pain intensity was 0.99 (<i>p</i> = 0.012).</p

Coupling functions for the nonlinear models.

<p>a) Coupling function for the CLMM and n = 1 iteration. b) Coupling function for the CLMM and n = 2 iterations. c) Coupling function for the CLMM and n = 3 iterations. d) Coupling function for the CSEM.</p

Coupling scheme for the CSEM.

<p>Gaussian white noise is used as input (channel 1). The data is then time-shifted by the interaction delay of δ = 6 samples, passed to the sigmoid coupling function and independent white noise is added to generate channel 2 and so forth for channels 3 and 4. External white noise (not shown) is added to all channels. Direct and indirect couplings are indicated by solid and dotted arrows, respectively.</p

Results for the CLMM.

<p>False detections in percent for different branches of CLMM reflecting different degrees of nonlinearity for a) FNDC, b) FNIC, and c) FP. d) Delay deviation in samples for different degrees of nonlinearity. LP: low-pass filter, HP: high-pass filter, Dec: decimation, X i: ith branch of the CLMM, All: average results for all degrees of nonlinearity. Asterisks indicate results significantly different from control (a-c: Fisher’s exact test, p < = 0.05, Bonferroni corrected, d: Wilcoxon rank-sum test, p < = 0.05). Error bars indicate standard deviation.</p

Group delay for different cut-off frequencies of a Butterworth low-pass filter.

<p>a) Group delay as a function of frequency for low-pass filter of 320 Hz (bottom), 160 Hz (middle) and 80 Hz (top). b) Mean group delay over pass-band frequency. lp: low-pass. Error-bars indicate standard deviation.</p

Mean power spectra of channel 2 (source) and channel 3 (target) low-pass filtered at 80 Hz.

<p>The mean is taken over 20 trials x 100 datasets.</p

False detections in percent for the Kus-model.

<p>LP: low-pass filter, HP: high-pass filter, Dec: decimation. Asterisks indicate results significantly different from control (Fisher’s exact test, p < = 0.05, Bonferroni corrected).</p

Delay deviation in samples for the Kus-model and increasing low-pass filter orders.

<p>Asterisks indicate results significantly different from control (Wilcoxon rank-sum test, p < = 0.05, Bonferroni corrected). Error bars indicate standard deviation.</p

Analyzed preprocessing types.

<p>Analyzed preprocessing types.</p