Neuron: A specialized cell that transmits nerve impulses, a nerve cell.
Membrane potential: The difference in electrical potential between the interior and exterior of the nerve cell.
Resting membrane potential: The membrane potential when a nerve cell is at rest (approximately -70 mV).
Threshold potential: The critical level the membrane potential must be depolarized to initiate an action potential (Typically -50 mV to -55 mV).
Action potential: The change in electrical potential associated with the passage of an impulse along the membrane of a nerve cell (peaks at around +40 mV). This is how nerve signals are transmitted, the fundamental mechanism of the brain.
Anode: The positively charged electrode.
Cathode: The negatively charged electrode.
Depolarization: Loss of the difference in charge between the interior and exterior of nerve cell.
Hyperpolarization: Increase of the difference in charge between the interior and exterior of nerve cell.
Neuronal excitability: The ease at which a neuron can develop an action potential from an incoming signal or stimulus. Excitability can be modulated by varying the resting potential of the nerve cell with respect to the threshold potential.
Phosphene: A temporary and benign flash of light that can be seen when electrodes are placed too close to the eye.
An Overview of tDCS:
Transcranial Direct Current Stimulation or tDCS, is a cheap, non-invasive, painless and safe form of brain stimulation. The technology involves the use of a low direct current between 1-2 mA, delivered to targeted areas of the brain via electrodes on the scalp. Electrical stimulation performed in this way can be used to either “excite” or “inhibit” neuronal activity at the target area. At the site of anodal stimulation (the positive electrode) nearby neurons are excited, whereas at the site of cathodal stimulation (the negative electrode) neuronal activity is inhibited. Many applications of tDCS are currently being explored, suggesting possible treatments for: depression, schizophrenia, aphasia, addiction, epilepsy, chronic pain, attention and motor rehabilitation. Studies have also demonstrated cognitive improvement in some patients being treated with tDCS.
tDCS Safety and Side Effects:
When used properly and in accordance to established safety protocols, tDCS is considered a safe form of brain stimulation with minimal risks of injury. Any adverse effects appear to be limited to temporary tingling, itchiness and redness at the site of stimulation (where electrodes are positioned). By slowly ramping up to the desired current, possible side effects such as headaches, irritation and light headedness can also be reduced or avoided. When electrodes are placed too close to the eye, user may experience phosphenes. If safety protocols are not followed, standard skin burns may occur.
For a more comprehensive look at tDCS safety guidelines and industry standards, Click Here to read a publication by Bikson et al., on the Engineering principles, regulatory statutes, and industry standards for wellness, over-the-counter, or prescription devices with low risk.
Your Neurons and tDCS:
tDCS changes the resting membrane potential of local neurons at the targeted area of the brain. During anodal stimulation, the resting membrane potential is depolarized by the conventional inflow of positive current (physical outflow of electrons). The membrane potential of the neurons in this state is closer to the threshold potential required to elicit an action potential, therefore anodal stimulation acts as a “primer” that increases neuronal excitability.
Conversely, cathodal stimulation hyperpolarizes the local neurons at the targeted area of the brain due to the conventional outflow of positive current (physical inflow of electrons). In this state, the membrane potential of the neurons are further from the threshold potential that elicits an action potential, this decreases neuronal excitability.
Regulatory Status of tDCS:
In the EU, tDCS is approved for the treatment of pain and depression.
In the United States, tDCS has an FDA (Food and Drug Administration) regulation status of “investigational”; this gives no indication of efficacy, it just means the FDA has not yet issued an opinion on tDCS. Because of this, companies in the United States are not allowed to market their tDCS devices with medical treatment claims such as “treatment for depression” or “treatment for epilepsy”. However, doctors in the United States are allowed to provide tDCS as a form of off-label treatment, that is, treatment that has not yet been approved by the FDA for the given indication. tDCS devices can also be readily obtained for home treatment and personal use; again, due to the FDA status of “investigational”, these devices do not guarantee or make any claims toward the treatment of any given indication.
Where Do I Place Electrodes?
tDCS electrode placement is typically based off the established 10-20 EEG system for mapping brain locations on the scalp. This system is internationally recognized and may also be referred to as the 10-10 system. The 10 and 20 refers to the actual distances between adjacent electrodes being either 10% or 20% of the total front to back or left to right distance of the skull. Each electrode position has a letter and number associated with it. The letter represents the lobe at that location, F (Frontal), P (Parietal), T (Temporal), or O (Occipital). The number represents the hemisphere, with even numbers for the right hemisphere and odd for the left hemisphere. Click here for a detailed step by step guide with instructional videos on electrode use and placement.
Where can I get a tDCS Device?
There are many distributors and manufacturers of tDCS products all over the world where you can obtain tDCS devices from. Click here for an in depth comparison where we review and breakdown the many tDCS options on the market.
Want To Learn More?
The videos below held at a summit on tDCS at UC-Davis Center for Mind and Brain will help provide a deep understanding about this exciting technology.