ANALGESIC EFFECTS OF EEG ALPHA-WAVE ENTRAINMENT ON ACUTE AND CHRONIC PAIN

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Abstract

Pharmacological treatments for pain show limited analgesic benefits when compared with placebo. Neuro-modulatory approaches, such as mindfulness meditation and neurofeedback training show more promising effects, but are time consuming and difficult to complete. Neural entrainment provides an almost instantaneous increase in EEG power of the stimulated frequency, achieved with minimal effort through visual flicker stimuli or auditory binaural beats. EEG recorded alpha power displays a reproducible inverse relationship with pain perception. Hence, the main objective of this PhD thesis was to develop an analgesic alpha entrainment intervention: increasing alpha power with the aim to reduce the perception of acute pain in healthy volunteers and chronic pain patients.Prior to attempting to modulate pain, pilot work assessing the ability to entrain alpha power is reported in Chapter 3. A checkerboard stimulus was used to visually entrain frequencies across the alpha band from 7Hz – 14Hz, resulting in a significant power increase at 10Hz and 11Hz. With the goal to reduce behavioural and electrophysiological responses to a moderately painful stimulus, EEG alpha entrainment at 8Hz, 10Hz and 12Hz through auditory binaural beats (in Chapters 4 and 5), and visual flashing LED goggles (in Chapters 4, 6 and 7) was then attempted. A significant reduction of pain ratings was found following both the visual and the auditory alpha stimulation across all three frequencies in Chapters 4,5 and 6. Chapter 5 revealed a significant alpha power increase following 10Hz and 12Hz auditory stimulation. The laser-evoked potential’s (LEP) N2 peak reduced significantly following 10Hz auditory entrainment and the P2 peak reduced significantly across all auditory entrainment conditions. In Chapter 6, alpha power entrained significantly at 8Hz and 10Hz. The P2 peak reduced significantly following the 10Hz visual stimulation. Source analysis showed the precuneus and posterior cingulate cortex might mediate alpha entrainment-induced reductions in LEPs and pain ratings. The paradigm used in Chapter 6 was repeated in osteoarthritic patients in Chapter 7. Significant reductions in pain ratings were observed following all three alpha stimulation sessions, despite a lack of alpha power increase. A significantly reduced response in the P2 peak was also observed following the 12Hz visual stimulation. Decreases in P2 source activity in the posterior insula suggest a functional role in the reduction of pain intensity triggered by alpha stimulation. A significant reduction in the electrophysiological response and the perception of moderately painful stimuli can be achieved through visual or auditory entrainment across the alpha band range, in both healthy volunteers and osteoarthritic patients. The findings from this PhD thesis provide a solid foundation for further investigation of alpha based neuro-modulation as an analgesic intervention.

Keyword(s)

EEG; pain

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