Transcranial Direct Current Stimulation (tDCS) is a form of non-invase neurostimulation that delivers a constant low level current to the brain through the use of electrodes placed on the scalp. This neuromodulation technique uses a steady current between 1 - 2 mA delivered through electrodes to targeted regions of the brain to modulate brain function. Using different electrode configurations, tDCS can be used to either excite or inhibit neuronal activity in the targeted region. Unlike transcranial magnetic stimulation (TMS), the current used in tDCS is not strong enough to trigger an action potential but rather effects the neurons resting membrane potential. When applying anodal (positive) stimulation, the electrode is used to faciliate depolarization of the neurons resulting in excitatory stimulation. Conversely, during cathodal (negative) stimulation, the electrode is used to induce hyperpolarization of the neurons resulting in inhibitory stimulation.
The positioning of the electrodes is used to determine the flow of current through different regions of the brain. These different electrode placements are called montages. Depending on the montage used, different regions of the brain are targeted to elicit the various desired effects. In order to understand the electrode placements outlines in the available montages it is necessary to understand the International 10-20 EEG positioning system, further explained here. This system helps map out the locations on the head allowing the user to correctly position the electrodes. When the electrodes are placed on the head they are held in place by headgear. This headgear is very important in ensuring a reliable and reproducable stimulation session. There are many options available but many users, including universities and clinics running trials, prefer the Caputron Universal Strap. This headgear provides ruler markings directly on the strap allowing you to quickly and accurately ensure your electrodes are placed in the correct location. Further information on the types of electrodes and how to properly care for them can be found on our Electrode Guide.
Conventional tDCS montages use two electrodes: the Anode electrode and the Cathode electrode. The Anode electrode has a positive voltage relative to the Cathode electrode. Current enters the body under the Anode electrode, flows through the brain, and exits the body at the Cathode electrode. By controlling the position of the anode and cathode electrode, the current flow through the brain can be targeted. Reliable current delivery and reproducible electrode placement is therefore critical for reproducible tDCS outcomes.
As tDCS is an investigational technique, it is the responsibility of the user to determine the appropriate tDCS protocols and dose. While tDCS is still investigational, research indicates that it has several advantages in the treatment of patients with a large variety of neurological and psychiatric disorders. tDCS safety is supported by medical literature to have common side effects limited to mild and reversible skin irritation, when using standard tDCS protocols and guidelines.
Researched tDCS Montages - tDCS technology is continuously being researched around the world. These links reference tDCS montages of various indications being explored and easily reproduced using the Caputron Universal Strap
When choosing a tDCS device it is important to ask the following questions:
Timer - Does the device have a built in timer that will alert you when a session is over, ensuring you do not over stimulate?
Low Battery - Will the device let you know when the battery is low and will not have enough voltage to deliver a complete stimulation?
Ramp Up/Ramp Down - Does the current on the device automatically ramp up at the start of the session and ramp down at the end of the session? This is important to avoid lightheadedness which could be caused by a quick onrush of current.
Steady Current Output - Does the device provide a steady and accurate delivery of current? Is it able to adjust to the constanttly varying resistance of the skin and internally regulate the voltage to keep the current steady?
Voltage - Does the device have enough voltage to ensure it can overcome the resistance of the skin and provide 2 mA of stimulation? Using Ohms Law V = IR and an average skin resistant of 10K ohms, the device would need atleast 20 Volts to be able to deliver 2 mA of current.
Use Caputron's comparison table to quickly view the different features of the most commonly available tDCS devices, Caputron tDCS Device Comparison Table.