[EEG] Lightning made me do it

[Josh Bailey]

http://www.technologyreview.com/blog/arxiv/25166/

Magnetically-Induced Hallucinations Explain Ball Lightning, Say Physicists

Transcranial magnetic stimulation (TMS) is an extraordinary technique 
pioneered by neuroscientists to explore the workings of the brain. The 
idea is to place a human in a rapidly changing magnetic field that is 
powerful enough to induce currents in neurons in the brain. Then sit back 
and see what happens.

Since TMS was invented in the 1980s, it has become a powerful way of 
investigating how the brain works. Because the fields can be tightly 
focused, it is possible to generate currents in very specific areas of the 
brain to see what they do.

Focus the field in the visual cortex, for example, and the induced eddys 
cause the subject to 'see' lights that appear as discs and lines. Move the 
the field within the cortex and the subject sees the lights move too.

All that much is repeatable in the lab using giant superconducting magnets 
capable of creating fields of as much as 0.5 Tesla inside the brain.

But if this happens in the lab, then why not in the real world too, say 
Joseph Peer and Alexander Kendl at the University of Innsbruck in Austria. 
They calculate that the rapidly changing fields associated with repeated 
lightning strikes are powerful enough to cause a similar phenomenon in 
humans within 200 metres.

To be sure, this is a rare event. The strike has to be of a particular 
type in which there are multiple return strokes at the same point over a 
period of a few seconds, a phenomenon that occurs in about 1-5 per cent of 
strikes, say Peer and Kendl.

And the observer has to be capable of properly experiencing the 
phenomenon; in other words uninjured. "As a conservative estimate, roughly 
1% of (otherwise unharmed) close lightning experiencers are likely to 
perceive transcranially induced above-threshold cortical stimuli," say 
Peer and Kendl. They add that these observers need not be outside but 
could be otherwise safely inside buildings or even sitting in aircraft.

So what would this kind of lightning-induced transcranial stimulation look 
like to anybody unlucky enough to experience it? Peer and Kendl say it may 
well look like the type of hallucinations induced by lab-based tests, in 
other words luminous lines and balls that appear to float in space in 
front of the subject's eyes.

It turns out, of course, that there are numerous reports of these types of 
observations during thunder storms. "An observer reporting this experience 
is likely to classify the event under the preconcepted term of "ball 
lightning"," say Kendl and Peer.

That's an interesting idea: that a large class of well-reported phenomenon 
may be the result of hallucinations induced by transcranial magnetic 
stimulation.

A difficult idea to test, to be sure, but no less interesting for it. And 
it raises an important question: in what other circumstances are ambient 
fields large enough to trigger hallucinations of one kind or another?

-- 
Josh Bailey (josh at anarkiwi.com)