  The electromagnetic pulses of rare long (order of seconds) repetitive
lightning discharges near strike point (order of 100m) are analyzed and
compared to magnetic fields applied in standard clinical transcranial magnetic
stimulation (TMS) practice. It is shown that the time-varying lightning
magnetic fields and locally induced potentials are in the same order of
magnitude and frequency as those established in TMS experiments to study
stimulated perception phenomena, like magnetophosphenes. Lightning
electromagnetic pulse induced transcranial magnetic stimulation of phosphenes
in the visual cortex is concluded to be a plausible interpretation of a large
class of reports on luminous perceptions during thunderstorms. APPENDIX
(Erratum and Addendum by J. Peer, V. Cooray, G. Cooray and A. Kendl): The
comparison of electric fields transcranially induced by lightning discharges
and by TMS brain stimulators via View E = - dA/dt is shown to be inappropriate.
Corrected results with respect to evaluation of phosphene stimulability are
presented. For average lightning parameters the correct induced electric fields
appear more than an order of magnitude smaller. For typical ranges of stronger
than average lightning currents, electric fields above the threshold for
cortical phosphene stimulation can be induced only for short distances (order
of meters), or in medium distances (order of 50 m) only for pulses shorter than
established axon excitation periods. Stimulation of retinal phosphene
perception has much lower threshold and appears most probable for lightning
electromagnetic fields.
