Traditionally, neurology tends to look at disease of the nervous system as black and white with one side being optimal neurological function and the other being neurological disease such as tumors, strokes etc.  Functional Neurology looks at dysfunction of the nervous system as different shades of gray looking for subtle changes in the nervous system before they become distinct pathologies.  You will often hear it said by functional neurologist that neurons need fuel and activation in order to thrive and survive.  Fuel can be defined as oxygen, glucose and essential nutrients.  Activation refers to stimulation of the nervous system which causes changes in the structure and metabolism of the nerve cell.