Cortical nociceptive processes are reduced by visual alpha-band entrainment in the human brain

Acute noxious stimuli induce a suppression of cortical alpha activity, yet little is known about whether increasing alpha activity affects the processing of noxious stimuli. We have previously shown that visual alpha stimulation reduces experimental pain. Here, we demonstrate that increasing alpha power causes a reciprocal suppression of acute nociceptive processing.

We attempted to increase cortical alpha activity through visual entrainment at 8 Hz, 10 Hz and 12 Hz to investigate the influence on the electrophysiological pain response. Moderately painful laser-heat stimuli were delivered following 10 minutes of visual entrainment across the alpha range.

Alpha power increased significantly relative to the 1 Hz control condition following 8 Hz and 10 Hz visual stimulation. Significant reductions in the P2 peak amplitude of the laser-evoked potential were found following visual entrainment at 10 Hz; the frequency stimulation resulting in the largest reduction in pain perception. Source analysis revealed that, following the 10 Hz stimulation, sources of increased alpha power and decreased nociceptive processing overlapped in precuneus and posterior cingulate cortex, with further reductions in nociceptive processing in insula cortex.

As far as we are aware, this is the first study to provide direct evidence that experimental induction of increased alpha power suppresses the cortical processing of acute pain.

While it is known that visual stimulation can increase the brain's oscillatory alpha rhythms, here, we show that this increase in alpha power occurs alongside reduced cortical processing of nociception, as measured with EEG. This establishes an objective marker of alpha entrainment-based analgesia that may be useful in the development of neuromodulatory treatments for clinical pain.