Gamma Brain waves 

Gamma waves are usually found in higher processing tasks as well as cognitive functioning. Gamma waves are  involved in learning, memory and information processing. the 40 Hz gamma wave are considered essential relating to perception and learning new things. People having mental deficiencies and learning disorders often have lower gamma activity than average

• Frequency range: 40 Hz to 100 Hz (Highest)
• Too much: Anxiety, high arousal, stress
• Too little: ADHD, depression, learning disabilities
• Optimal: Binding senses, cognition, information processing, learning, perception, REM sleep
• Increase gamma waves: Meditation
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• Source : mentalhealth