Acetylcholine (ACh) plays an important role in cognitive function and muscle atonia in rapid eye movement (REM) sleep. This quantitative study used surface electromyography (sEMG) to investigate changes in muscular activity, which may indicate a deficiency of ACh among patients with cognitive impairment. We recruited 9 controls without dementia, 6 patients with mild cognitive impairment (MCI), and 6 patients with mild Alzheimer's disease (AD). None of the participants had sleep complaints, and all AD patients were receiving cholinesterase inhibitors. Subjects underwent polysomnography (PSG), including sEMG of the leg muscles, which was analyzed using root mean square (rms), mean frequency, and peak frequency. The average rms values during REM sleep among the control, MCI, and AD patients were 0.553 ± 0.177, 2.886 ± 2.865, and 0.909 ± 0.822, respectively. The average peak frequencies during REM sleep in control, MCI, and AD patients were 0.402 ± 0.758, 30.524 ± 32.237, and 0.566 ± 1.153, respectively. The average mean frequencies during REM sleep in control, MCI, and AD patients were 8.849 ± 6.071, 34.530 ± 25.564, and 9.553 ± 6.308, respectively. All rms, mean frequencies, and peak frequencies increased significantly (p <0.05) in MCI patients. A deficiency of ACh may result in an increase of sEMG activity in MCI patients. Because cholinesterase inhibitors are capable of suppressing sEMG activity in AD patients, we speculate that an increase in sEMG activity is associated with a deficiency of Ach, which could be an early indicator of dementia.
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