If you hook up electrodes to the scalp, you can see the changes in electrical potential across the brain. This is what neurologists call an electroencephalogram. Neurologists can also look at electricity in the brain with electrodes that are planted deeper, as in deep brain stimulation.
Whether recording from the brain's surface or its depths, similar patterns begin to emerge. For one, the electrical signals that we measure are often rhythmic. Different parts of the brain have different rhythms. For example, the back of the brain has an electrical beat of about eight pulses per second when the eyes are closed. This is known as the alpha rhythm. When eyes are open, parts of the brain go faster, up to forty beats a second or more.
Studies using functional magnetic resonance imaging (fMRI) or magnetoencephalography (MEG) have showed that areas of the brain with similar rhythms are part of shared networks that allow the brain to do its job. Maybe our brain's dependence on rhythm helps explain the joy we find in music.
While rhythm is essential to how the brain normally functions, rhythm can also be involved with problems of the brain. For example, seizures involve extremely rhythmic activity that takes over part or all of the cerebral cortex. Tremor is rhythmic by definition. While all of us have some degree of tremor, it can get out of hand in cases like Parkinson's disease and essential tremor.
Just how our brain transforms rhythmic electrical signals into what we feel, say and do is one of neurology's great mysteries, and an active area of research. To learn more about rhythm and the brain, start here: Your Musical Mind.