Talk about a flash of insight. Lightning strokes could stimulate people’s brains and cause them to hallucinate bright blobs of light the same way a medical procedure that applies magnetic fields to the brain does, two physicists propose. The findings could help explain some reports of “ball lightning,” mysterious floating orbs that have been reported for centuries but are poorly understood. A paper describing the idea will appear in Physics Letters A.
“We don’t claim to have a solution for the mystery of ball lightning,” says study coauthor Alexander Kendl, a plasma physicist at the University of Innsbruck in Austria. “But this is a possible hypothesis.”
Lightning forms when electrical charges become physically separated in a storm cloud and build up electrical potential between them, which is then discharged in the sudden bolt. Strokes typically come in clusters. In some cases, Kendl says, they can come extremely rapidly: something like 20 to 60 lightning strokes, each on the order of 100 milliseconds long, raining down over the course of several seconds.
These rare repetitive strokes, Kendl’s team found, generate magnetic fields that are very similar — in strength and in how they rise and decay over time — to those used in a brain-stimulation technique called transcranial magnetic stimulation, or TMS.
TMS applies magnetic fields to the brain to treat neurological and psychiatric conditions like stroke and depression. While the stimulation is being applied to the visual cortex, some patients report seeing blobs of light in their field of vision. Such experiences, of seeing light when light is not actually entering the eye, are known as phosphenes. (The patterns of light you see when you rub your closed eyes hard are another type of phosphene.)
Working with Innsbruck graduate student Josef Peer, Kendl calculated that repetitive lightning strokes would trigger phosphenes “astonishingly well.” A person would need to be within about 200 meters of the lightning to experience the effect.
But Thomas Kammer, a TMS expert at the University of Ulm in Germany, isn’t convinced. Patients report seeing many different kinds of TMS-induced phosphenes, but they don’t generally mesh with descriptions of ball lightning. “I cannot imagine that long-lasting visual phenomena as described with ball lightning might be based on induced phosphenes,” Kammer wrote in an e-mail.
Scientists have proposed before that ball lightning reports could be ascribed to visual hallucinations, but the new study is the first to quantify the phenomenon in such detail and relate it to a known phenomenon. In 2008, researchers in Sweden proposed that magnetic fields associated with lightning could affect neurons in the part of the brain known as the occipital lobe, setting off epileptic seizures and inducing visions later described as ball lightning.
“Evidence is mounting that most, if not all, of ball lightning observations are created by the interaction of lightning-generated magnetic fields with the human brain,” says a coauthor of that study, electricity expert Vernon Cooray of Uppsala University in Sweden.
Scientists have struggled for centuries to explain ball lightning, in part because reports of it are so varied. It is often described as a yellowish ball that hovers around eye height for a couple of seconds before vanishing. But other reports describe ball lightning of various colors moving rapidly, fizzling or even exploding; some say it is accompanied by a sharp smell or sound.
The diversity of descriptions, Kendl says, suggests ball lightning may be a catchall term describing many different types of experience.
