A leak in your roof can travel a circuitous route through rafters and joints before it surfaces three rooms away as a creeping stain on the ceiling over your sofa. Symptoms of illness or injury are like the stain, the observable thing that gets your attention and prompts you to investigate further.

Working backward from a symptom to find the cause is the perpetual puzzle of science and medicine. It is particularly so in neurology, with the interconnected complexities of the brain itself, the vast domain of the nervous system, and the mix of hormones and other fluctuating neurochemistry. In any case, the sooner you can track an observable symptom successfully to the source, the sooner you can identify the most effective treatment options