It's everything.
"All life is vibration.

When it ceases, that is death--and even dead matter vibrates.

All our senses depend on vibration.

Everything we feel, see, hear, taste, comes to our knowledge through vibrations.
And the receptive force in us is vibration, too.

The brain is just one great, central ganglion for the taking in of vibrations.
"The secret of life, of the universe itself, is vibration.