This device has some modes built-in, based on Transcranial Electric Stimulation. Including one based on MIT Dormio for influencing dreams.
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Here you can see the menu selection for the tACS continuous mode. In this sub-menu, you can choose the frequency, which is controlled with a potentiometer. The range frequency is from 1-100Hz, defined in the program code. Also, you can choose the desired current intensity (setpoint), it is defined from 0.5mA to 3.0mA, a safe range for TES. More explanation in other updates.
This is the main menu, where you can choose tACS/tDCS modes and enter their sub-menus for choosing between the modes (continuous time, timed, onset mode for dream influencing, and sham). There is also a section called GSR Monitor. This section shows a real time graphic to measure the Galvanic Skin Response, as you may know, skin conductance plays a role on identifying some factors such as emotional related with psychophysiological, some of you may know that lie-detector machines uses this principle, but here, the goal is to have at least one physiological signal measurement from the subject. This would be also helpful for identifying patterns in emotional changes during a session, before a session or after, this helps identifying effects on TES and its implication in other biological processes.
Here you can see an active tACS session. Valuable information is shown. The frequency is displayed (frequency is selectable due to the experiment protocols, various frequencies can lead to different effects on different areas on the brain). The time is always displayed in EVERY mode, whether timed or continuous, the "E" stand for "State", which says Active and Ramping Up, the ramp is 5 seconds, as you may know in most of common protocols, there is always a smooth ramp of the current delivering, going from zero to the set target. The SCALYo, is the value of the microcontroller DAC generating the sinusoidal waveform signal, this means, the amplitude. According to the desired current intensity, the amplitude of the sine wave will be adjusted by the constant current system to reach the desired set by the user. Here is a 1.5mA target and 1.5mA real-time measuring of 1.5mA flowing through the scalp. As said before, the PID tune-fine allows to not to exceed the overshoot or get wrong values/measurements.
Impedance thing: we know that for those TES devices, the total impedance plays a crucial role. A human impedance can even reach more than 100Kohm. This is a problem when we want a constant current source so we can deliver to the brain areas the exact desired current. For this, an IC and a R_shunt is used to constantly monitor the current flowing through the electrodes to the brain. Through software, it is precisely tuned (by PID fine-tuning in both modes tACS and tDCS), to always deliver the desired current no matter how the impedance can change in the process, if it is too low, it will always match the current with the one set in the target, as so as if the impedance increases for some reason described before, the device will mantain the target current. This is important mainly for: one: subject safety, if impedance drops too low, there is a chance of a high current flow to the head, and two: current delivery effectivity, if impedance goes too high, the system will try to mantain the current in the target set. If electrodes have a bad contact/placement, as you can see in the image, a warning will pop up telling "High IMPEDANCE?" and the real-time measured current (the one above the target), is zero (or very low, 0.1mA), meaning you must check the electrode contact/wire connection.
This is the tDCS mode in continuous time mode. As you can see, also intensity can be set with a potentiometer, defined from 0.5mA to 3.0mA also. Here Frequency is not needed as you may know that DC doesn't oscillate. Here you just set the desired frequency and set start. For tDCS, it is just the set intensity, in tACS, however, the values shown in screen (in mA), are the Ip values, so making calculations, if you set a value of 1.5mA, it will be Ipp = Ip * 2 = 3.0mApp. For RMS value, it is Ip / √2, so, 1.5mA / √2 = 1.06mA RMS, which is within the stablished safe limits internationally. The maximum RMS set internationally, is 2.1mA RMS, which you can achieve with 3.0mA. Given IRMS = Ip / √2, 3.0mA / √2 = 2.1mA RMS. The good thing here, is that current will be constant no matter the impedance of subject (Z) which can varies by some factors, such as physiologycal state, as so as psychological, electrode impedance, placement, electrode contact and quality. This will be explained further.
Sylar Robert Jones
Bruce Land
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