Investigating the Effect of Distraction on Pain-Related Ongoing Neural Oscillations

Background & Aims Ongoing neural oscillations have been shown to be modulated in the theta, alpha and beta frequency bands by sustained nociceptive stimuli, at the frequency of stimulation (FoS) 1-3. These findings suggest a relationship between nociception and ongoing oscillations, but it remains unclear whether these modulations play a significant role in the perception of pain. If this is the case, cognitive processes known to affect pain perception should also affect these ongoing oscillations. To investigate the relationship between pain perception and ongoing oscillations, we assessed the effect of distraction – an attentional state known to affect pain perception 4 – on both perceived pain intensity and the modulation of ongoing oscillations measured using scalp electroencephalography (EEG). More specifically, we hypothesized that a distraction task would lead to a decrease in the perceived intensity of a painful thermonociceptive stimulation, concomitant to a decrease in amplitude of the modulation of ongoing oscillations exerted by the stimulation. Methods Prior to the investigation, we conducted a behavioral pilot study on 21 healthy young subjects (24.7 ± 2.85 years old, 9 males) to assess the efficacy of the distraction task. Subjects were exposed to two conditions: baseline (no task) and distraction. The task consisted of continuously subtracting 7 from a 3-digit starting number throughout the stimulation 5 and to report the final number after the end of the trial. Very slow periodic sustained thermonociceptive stimuli were used, at a frequency of 0.2 Hz (range: 35 - 50°C) over a duration of 75s per trial 2. After each stimulus, the subjects provided a rating of the intensity of the stimulus on a scale from 0 to 10 (0: no pain, 10: most painful imaginable). A linear mixed model analysis investigating the effect of condition showed that the distraction task led to a significantly lower rating of perceived pain intensity compared to baseline (β = -0.90, t(42) = -4.30, p<0.001), indicating that the task succeeded in diverting subjects’ attention from the thermonociceptive stimulation. We therefore plan to use a similar paradigm (baseline vs. distraction during sustained periodic 0.2 Hz thermonociceptive stimulation) in the main investigation. This poster presents pilot data for this experiment. Subjective intensity of perception of the applied stimuli was assessed after each trial using a visual analog scale (min.: “no perception”; max.: “most intense perception imaginable”). EEG data was acquired using a 64-channel setup and the modulation of ongoing neural oscillations was assessed in the theta, alpha and beta frequency band using a “frequency-tagging of ongoing oscillations” approach 1,2. This approach is an extension of the commonly used frequency-tagging 6, applied to ongoing oscillations by filtering the data for the respective frequency band and estimating the signal envelope using a Hilbert transform before applying a discrete Fourier transform. The EEG data was averaged across subjects and conditions, and the average of all channels was computed for further analysis. Linear mixed models were used to assess the effect of condition on 1) perceived intensity of the stimulation, 2) periodic response of the EEG signal and 3) the modulation of ongoing modulations in the different frequency bands. Eight healthy subjects (23.2 ± 2.25 years old) took part to this pilot. Results The subjects rated the intensity of the thermonociceptive stimuli during the distraction task as significantly lower compared to baseline (β = -1.36, t(275)= -5.28, p<0.001) [Figure 1]. A periodic response of the EEG signal (amplitude significantly different from zero) at the FoS was found for both conditions, which were comparable in their amplitudes. A periodic modulation of ongoing oscillations at the FoS was found in all frequency bands (theta, alpha and beta). Moreover, the theta frequency band showed a significantly smaller response during distraction compared to baseline (β = -0.01, t(6.41)= -3.20, p