General Notes:
To design a custom stimulation protocol, select the "Advanced" configuration in NIC. This mode allows you to define key parameters such as current intensity, phase, and frequency.
tDCS Protocol:
To apply tDCS, assign a positive current to the desired stimulation channel.
Example in picture: Channel 13 set to +600 µA
To define the return channels, assign negative currents.
Example in picture : Channel 14 and Channel 24 set to -300 µA each.
Important: The sum of all stimulation and return currents must equal zero to ensure current balance in every moment.
tACS Protocol:
To apply tACS, assign an amplitude to the stimulation channel and specify the desired frequency.
Example in picture: Channel 13 set to +600 µA and 10Hz
To configure the return channel, set the same amplitude but assign a phase shift of 180°.
Example in picture Channel 14 and Channel 24 set to 300 µA, 10 Hz and a phase shift of 180º each.
For every current signal with a given frequency and no phase shift, there must be one or more currents of the same frequency but with a 180° phase shift, whose sum exactly cancels out the amplitude of the original signal all the time.
As with tDCS, ensure the total current across all channels equals zero.
tACS and tDCS protocol simultaneously.
If a protocol combines both direct and alternating currents, the previously described steps must be followed. The most important rule is that the total sum of currents must always equal zero at every moment in time.
For example, if 300 µA of direct current and 200 µA of alternating current at 80 Hz are applied to the active electrode, then the return electrode must have –300 µA of direct current and 200 µA of alternating current at 80 Hz with a 180° phase shift, to ensure electrical balance.
tRNS Protocol:
In tRNS, you can configure two main parameters:
Standard Deviation (STD) of the noise signal, which can go up to a maximum of 650.
tRNS filtering, which defines the frequency range of the random noise.
The current values will fluctuate within approximately ±3 times the STD.
For example, if the STD is set to 650, the current will randomly vary between –1950 µA and +1950 µA.
If no bandpass filter is configured, the device will deliver random current fluctuations across the full default frequency range of 0–500 Hz.
You can modify this range by selecting a specific filtering option in the tRNS filtering settings, where four modes are available:
None – Full spectrum (0–500 Hz)
Low – Low-pass filter
Band – Band-pass filter
High – High-pass filter
Each option allows you to tailor the frequency content of the noise according to your stimulation protocol.
Anodal and cathodal stimulation
In anodal stimulation, the active electrode is the anode (+). The current flows from the anode to the cathode, slightly depolarizing the neuronal membrane beneath the active electrode. This depolarization brings neurons closer to their firing threshold, increasing cortical excitability in that region. Anodal stimulation is typically used when the goal is to enhance brain activity, for example to facilitate cognitive or motor processes such as post-stroke motor rehabilitation or the acquisition of new skills.
In contrast, cathodal stimulation uses the cathode (–) as the active electrode. Here, the current flows in the opposite direction, slightly hyperpolarizing the neuronal membrane under the electrode. This hyperpolarization moves the membrane potential further from the firing threshold, reducing cortical excitability. Cathodal stimulation is often applied when the aim is to inhibit excessive brain activity, as in cases of focal epilepsy or tinnitus.
Because anodal and cathodal stimulation have opposite effects on neuronal excitability, they can be used strategically to either enhance or suppress activity in targeted brain regions, making tDCS a flexible and valuable tool in both clinical and research settings.
If you design a protocol with one electrode as the return and the other as the stimulation electrode, and you designate the stimulation electrode as the cathode, the current flowing through that electrode will be negative, while the current through the return electrode will be positive. This is because, the current flows from anode → cathode. In other words, the stimulation electros is receiving the current.
On the other hand, if you designate the stimulation electrode as the anode, the current flowing through that electrode will be positive, and the current through the return electrode will be negative.
I recommend always designating the stimulation electrode as the anode, so the return electrode will automatically have a negative current.