Tuesday, February 16, 2010
AVE and Seizures
Roughly 1 in 10,000 adults and 1 in 4,000 children could have photic induced seizures. To induce seizures, neurologists use photic stimulators with Xenon strobe lights that flash very suddenly, usually within 50 microseconds at intensities of 10,000 to 300,000 lux. Several researchers have found that red-flicker light provokes an increased risk of photo-convulsive response (PCR) relative to other color wavelengths. It has been further found that the peak PCR occurs from red-light, square-wave stimulation (instant on - instant off) in the 15 to 20 Hz range. Ruuskanen-Uoti (1994) reported on a person who developed seizures while using a “light and sound” machine utilizing square wave stimulation delivered by red light emitting diodes (LEDs). However, it has been found that low levels of blue light will inhibit a seizure in the making.
In addition to increasing the chance of seizure, square wave light stimulation also generates odd harmonics in the brain. Therefore, when stimulating at 10 Hz, in the hopes of inducing meditation, a 30 Hz harmonic can be generated within the brain and trigger an anxiety/panic reaction in some people. This is why we use sine wave entrainment for frequencies at 10 Hz and lower – to actually induce meditation that the user wants – not anxiety. We don’t use square wave stimulation in any of our sessions (although it is possible to use in a user defined session with the Session Editor). Most other light and sound devices use square wave entrainment, as square waves are easy to make.
About 8% of those with a history of natural (non-photic) seizure are also photo-epileptic. Care must be taken when delivering photic stimulation, particularly to children. However, we have seen anecdotes where alpha (10 Hz) and/or SMR (14Hz) have settled down seizure quite a bit. When using visual entrainment (VE) to treat seizure, it must be done under the supervision of a qualified health-care professional with EEG monitoring. Typically, the spike-and-wave activity associated with seizure can be observed on the EEG before physical symptoms become apparent and the session can be stopped.
Auditory entrainment (AE) is a safe alternative for people who have a history of seizures or believe that they might be susceptible to seizures using photic entrainment. AE (using the pulsed sounds only) does entrain brain waves, but is not as powerful as visual and auditory entrainment combined. Firstly, there are over 1,000,000 incoming nerve fibres from each eye and about 10,000 incoming nerves from each ear. This huge difference between eye and ear input contributes to the reasons why VE can cause seizure while auditory entrainment is safe. A study by Frederick (1999) found that AE at 18 Hz (the only frequency they tested) increased brain activity by 21% whereas VE entrainment increased brain activity by 49% when measured at the vertex (top of head).
So, although VE is extremely effective, there is sometimes a need for caution; whereas AE, although less effective, is a very safe option.
We have an article on our web site with more information on the safety of using AVE and seizures. I would invite you to go to: www.mindalive.com/1_0/article%208.pdf.
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- dancing in the dendrites!