Alpha waves or alpha rhythms were a type of neuroelectric activity present in the brains of individuals who were either relaxed but awake or in the middle of REM sleep. They could be stimulated with an alpha-wave inducer. (DS9: "The Passenger")
Shortly before Luther Sloan died in 2375 his alpha waves attenuated, followed by a complete neural failure. (DS9: "Extreme Measures")
In 3189, an atomic scan was performed on the brain of Philippa Georgiou. The results of the scan revealed that her alpha rhythm had sinusoidal-like waves with a frequency range of 8-12 Hz. (DIS: "The Sanctuary")