Everything within and on the planet and its surface is surrounded by certain energy fields. These are light, gravitational, magnetic and electrostatic fields.
The most observable fields surrounding us is the magnetic field of the Earth, and the electrostatic field.
The electrostatic fieldis high voltage field that extends from the surface of the Earth all the way to the Ionosphere, ranging in between 300,000- 400,000 volts.
The magnetic field on the other hand, is subjected to regular pulsations low in magnitude, with frequencies starting from 0.1 to 100 cycles per second- with the average cycles ranging from 8 - 45 cycles per second.
Coincidentally, the average brain waves are also centered around 8-16 cycles per second. It is very plausible therefore, that the regular pulsating magnetic field of the Earth, stimulates normal brain wave rhythm.