Epilepsy is one of medicine’s great mysteries. The seizures that characterize the disorder are caused by electrical storms in the brain that are as hard to predict as squalls on the open sea. They can erupt early in life, for reasons that may be partly genetic, and they are common after head injuries. But scientists cannot identify an exact cause.

What they do know is that many patients’ brains have a “hot spot” where the seizures originate — and that removing that pinch of tissue can reduce the symptoms, often drastically. The challenge: finding that spot in each person.

Since the 1950s, surgeons worked by instinct and experience, stimulating points on the brain’s surface, guided by the patient. Yet in people like Ralph, they need not only to map the brain’s surface but to sound its depths. They made punctures in the top of his skull and threaded 11 probes deep into his medial temporal lobes, near an area called the hippocampus, about level with the ear.

And then they listened and waited for a seizure to occur.

That wait can take two to three weeks, and surgeons are using this period to study patients who are awake and responsive with electrodes smack dab in areas of the brain that are most important for learning and memory.

The hippocampus is the very seat of memory formation, and its importance emerged from the study of an epilepsy patient whose procedure went famously awry. Henry Molaison, known worldwide as H.M., had severe seizures until a surgeon removed the hippocampus from both hemispheres of his brain in 1953. In a series of experiments, Brenda Milner of the Montreal Neurological Institute and McGill University showed that, without those seahorse-shaped organs, H.M. could form no new memories for facts, figures or faces. This finding, the most important in modern brain science, opened the way for direct-recording experiments.