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In conventional neurofeedback we reward the increasing or the inhibiting of a targeted metric or bandwidth. This can be done because of the nature of the signal and equipment we use to measure it. The regular cycling of the sinusoidal signal can be measured by an alternating current amplifier. Tin and gold sensors can hold that signal steady.
ISF, however, is very slow and it ‘meanders.’ It does not present with the steady rhythmic beat that we see in the faster ranges. As we drop lower in frequency, the amplifiers that measure information using alternating current (AC) are unable properly pick up the signal. For the signal to be effectively read, it must be measured with a combination of a direct current (DC) and alternating current.
DC ‘clarifies’ the signal. With DC in the mix, minute changes in this fluctuating wave form become detectable to the amplifier and those changes are translated into a tone that is audible to the client. These changes are on the order of 0.1 millionths of a microvolt. This is a tiny signal that would be a flat line without DC. DC, however, animates the signal, and it becomes an undulating fluctuation. The information in those tiny changes has a powerful effect on the human cerebral cortex, specifically impacting the autonomic nervous system.
In contrast to tin, gold, or silver ear clips, silver/silver chloride (Ag/AgCl) sensors are able to hold the ISF signal steady due to the elevated concentration of chloride. Ag/AgCl electrodes keep resistance low and reduce the noise that can interfere using traditional electrodes.
The specialized equipment needed to perform ISF training is a factor of the minute signal and the speed of the ‘fluctuation.’ An AC amplifier and tin, gold or silver ear clips would simply be unable to accurately read the data to allow for effective training.