I am currently trying to start a research project, and this is the most important question that needs to be answered. I cant't move ahead without knowing the chemistry of the brain.
Cells in the brain communicate with each other through electrical (and chemical) signals. The electrical signals from millions of neurons add up, and can be detected from outside the skull. This is called electroencephalography.
The signals that are strongest when measured in this way are often periodic or oscillatory (i.e. wave-like), because similar electrical signals from many neurons support each other if they are active synchronously. In contrast, when neurons are firing in a disordered way, then their electrical signals can partially cancel each other out when measured from outside the skull.