Objective: Increased high-frequency EEG activity in patients with insomnia has been posited to reflect increased physiological activity, increased mental content, or increased muscle artifact. In the current study, the. impact of physiological arousal and increased EMG upon spectral EEG measures was examined. Methods: Thirteen normal young adults performed eyes-open and eyes-closed maneuvers in the following conditions: (1) Initial (performed immediately after calibrations); (2) following sitting up and lying down (SIT); (3) following standing up and lying down (STAND); (4) Following a 5-min walk around the building (WALK); (5) during a 5-min mental subtraction task (MATH); (6) During I min of gritting teeth (GRIT); and (7) During I min of clenching fists (CLENCH). Observations were performed during or immediately after manipulations (AROUSED) and repeated about 10 min later (RELAXED). Results: Significant increases in high-frequency spectral power were found in AROUSED vs. RELAXED conditions (significant at 26, 33, 36,40-42, 44, 46, and 48-49 Hz). Larger significant increases in spectral power were seen in the GRIT condition in the range from 24 to 50 Hz and to a lesser extent in the CLENCH condition. Spectral activity during the MATH condition was similar to that in the AROUSED condition. Heart rate was significantly increased during the GRIT and CLENCH conditions. Conclusions: In this study, gritting teeth produced large changes in spectral high-frequency power in the same range as produced by the other manipulations. The most parsimonious explanation for such data is that the increased high-frequency activity associated with various forms of arousal is not a specific cortical activity. However, because heart rate was also elevated during the GRIT condition, it implies that high-frequency spectral EEG power may still be a sign of increased central nervous system arousal, although the mechanism may be through increased muscle tension. (C) 2001 Elsevier Science Inc. All rights reserved.
