Your brain emits waves. There are five waves Delta, Theta, Alpha, Beta and Gamma. Delta [0.5-4Hz] waves are emitted when you are in deep sleep or when you can achieve transcendental meditation. Theta [4-7.5 Hz] waves are emitted when you are sleeping or when you are in deep meditation. It is said that you experience the most creativity when your mind is emitting Theta waves. Alpha [7.5-15Hz] waves are present when you are in a relaxed mood, deep thinking or light meditation. It is also said that intuitions come from an Alpha state. Beta [15-40Hz] waves are when you are awake and conscious. It is in your beta state that you can hear that nagging voice inside your head talking to you.
Buddhist monks have been known to emit the almost unheard of Gamma [40-100 Hz] waves as an outcome of transcendental meditation. Maharishi Mahesh Yogi made transcendental mediation famous world over. Scientists in Germany have recreated these waves in the form of sounds. While the jury is still out of whether listening to these sounds can positively impact your brain, I found it relaxing and stimulating. You need ear phones to listen because the sound waves are at differential frequencies and best heard with ear plugs. Some of the sounds that I like are linked here and here.