Global field power helps separate respiratory-related evoked potentials from EMG contamination

Respiratory-related evoked potentials (RREPs) were stimulated by brief (200 -ms) oral pressure pulses (-10 cmH(2)O) applied at the onset of inspiration in 12 subjects. Scalp potentials were measured at 30 sites on a rectangula r grid that encompassed the right side of the scalp overlying the somatosen sory cortex (SSC). Concurrent and significant masseter EMG (mEMG) activity was evoked by the pressure pulse, and we found correlational evidence for c ontamination of the RREP by the mEMG. The global field power (GFP) was used to provide a robust, reference-independent measure of SSC activation that provided partial insulation from mEMG contamination. The mean GFP from all subjects, reflective of afferent information from respiratory mechanorecept ors, showed a latency to onset of significant afferent SSC activity of simi lar to 25 ms. Scalp GFP activity during control experiments (absence of app lied pressure) was significant and may reflect ongoing afferent activity fr om inspiration.