EEG changes reflecting pain: is alpha suppression better than gamma enhancement?

Area of Science:

• Neuroscience
• Pain Research
• Electroencephalography (EEG)

Background:

• Cortical pain processing is often indicated by changes in alpha and gamma electroencephalographic (EEG) power.
• Gamma activity is considered a strong pain marker, but its overlap with muscle activity poses a challenge.
• Investigating EEG changes during both pain and muscle contractions is crucial for validating pain biomarkers.

Purpose of the Study:

• To compare alpha and gamma EEG activity during tonic pain versus voluntary facial grimaces.
• To determine if gamma activity's topography during pain is distinct from muscle-induced activity.
• To evaluate the potential of alpha and gamma power as objective pain biomarkers, considering muscle artifacts.

Main Methods:

• High-density EEG (128 electrodes) was recorded from 14 healthy participants.
• Participants underwent a cold pressor test (pain) and performed facial/nuchal contractions (grimaces).
• Scalp EEG power distributions (alpha and gamma) were analyzed and compared between conditions using topographical analysis.

Main Results:

• Pain significantly increased gamma power in fronto-temporal regions and decreased alpha power in the contralateral central scalp.
• Grimaces also increased fronto-temporal gamma power but did not affect central alpha power.
• The topographical distribution of gamma power was similar during pain and grimacing, while alpha power changes differed significantly.

Conclusions:

• Gamma power topography during pain overlaps with that induced by facial muscle contractions.
• Pain-related alpha power decrease in the contralateral central scalp is less affected by muscle activity.
• Alpha power modulation may serve as a more discriminant ancillary biomarker for pain processing.