From Serial Experiments Lain wiki
The Schumann resonances are mentioned in Layer 09. They are a set of peaks in the electromagnetic field spectrum of the Earth. In Serial Experiments Lain, it is proposed that these resonances can affect the human brain directly and provide a means to connect to The Wired without using any devices.
These resonances are what allow the Psyche chip to function. Masami Eiri modified Protocol 7 to allow people to connect to the Wired through the Schumann Resonances, and was fired from Tachibana General Laboratories as a result. It is possible that he led the Knights of the Eastern Calculus to distribute the Psyche chip to fulfill his ideal of connecting the human race into a neural network for the Earth.