What is tDCS Therapy? From Novice to Expert!

Transcranial direct current stimulation – tDCS for short – is a low-cost, non-invasive tool used to alter the excitability of particular brain circuits for its therapeutic benefits.

The Purpose of Brain Stimulation

Neuroscientists have, in recent times, had an increasing appreciation of the brain’s regional specialisation. That is, the idea that individual regions of the brain are responsible for specific functions. As a result, there has been growing interest in deliberately stimulating or inhibiting individual brain regions so as to target specific cognitive, sensory or motor functions.

The brain relies on electrochemical signals to communicate within and between regions. These signals travel through wire-like cells called neurones, which communicate with one another, often forming vast neural networks. Due to the electrical nature of the brain, by applying a controlled electrical current, the excitability of neurons within the target regions can be modulated. This modulation alters the firing patterns of these neurons and influences the strength and efficiency of their connections As you would expect, this has huge potential for altering brain function.

What is tDCS? How does it work?

One brain stimulation technique that has garnered a lot of attention is transcranial direct current stimulation (tDCS). Numerous studies have shown the ability of tDCS to powerfully alter activity patterns with observable outcomes on behaviour, mood and cognition. But what exactly is tDCS, and how does it work?

A key advantage of tDCS in comparison to other forms of brain stimulation is that it is non-invasive. Unlike invasive techniques such as deep brain stimulation (DBS), it does not require surgery or implantation of electrodes into the skull. Instead, it works by placing electrodes on the scalp or forehead, which are stimulated with a low-intensity, continuous electrical current. This current travels through the skull, altering the activity of the brain tissue underneath.

Traditional tDCS typically uses two electrodes on the scalp to deliver a steady flow of current. However, it is now becoming common in clinical trials to use several smaller positive and negative electrodes. The cortical regions in close proximity to the positively charged electrode(s) are excited, whilst inhibitory effects are observed in the brain regions below the negatively charged electrode.

Another key advantage of tDCS is its reversibility. Due to the low intensity of the current applied to the scalp during tDCS therapy, it is usually well-tolerated by most individuals with minimal side effects. However, this does not mean that tDCS is not a potent stimulus. While the effects of a single tDCS session may be modest and transient, repeated sessions over time can lead to cumulative effects and longer-lasting changes in brain function.

The cumulative effects of tDCS result from its ability to induce neuroplasticity. Repeated sessions of electrical stimulation can induce lasting changes in synaptic strength, neuronal excitability and connectivity within the brain.

Brain Regions Targeted by tDCS Therapy

Although which brain regions tDCS can target is limited by their proximity to the scalp, several regions in the cortex can be targeted. By far the most common region stimulated during tDCS therapy is the Dorsolateral Prefrontal Cortex (DLPFC). This is for several reasons:

• The DLPFC is a subregion of the prefrontal cortex involved in decision-making, working memory and cognitive control.
• It is particularly important for exerting conscious control over one’s own thoughts, emotions and level of autonomic arousal (anxiety/relaxation).
• Due to its role in mood control, the DLPFC is often targeted in depression treatment. Indeed, Flow Neuroscience’s device, developed for depression treatment, targets this region.
• Using tDCS therapy to stimulate the DLPFC can be used for more than just depression, however. For example, due to its role in cognition, tDCS of the DLPFC has also been applied for the purpose of cognitive enhancement!

In addition to the DLPFC, tDCS of other brain regions has shown success. These include:

1. The Motor Cortex: The motor cortex controls voluntary movement. Therefore, stimulating neurons in this region, tDCS can enhance motor learning and precision in individuals with motor deficits. It has shown success in combination with physical therapy in patients with stroke-related motor impairment and Parkinson’s disease. Stimulation of the primary motor cortex also appears to have efficacy in ameliorating acute pain.

• The Temporal Cortex: The temporal cortex plays a role in auditory processing, language comprehension and association. tDCS targeting this region may affect language skills, auditory perception, and memory functions.

• Somatosensory Cortex: Found in the parietal lobe, the somatosensory cortex processes sensory information from the body, including touch, temperature, and pain. tDCS applied to this area can modulate tactile perception, pain sensitivity, and somatosensory integration.

In order to target these regions, a customisable tDCS device is needed where you control the electrode placement. Options include the Brain Driver, NeuroMyst and the Flow Headset.

Therapeutic Applications of tDCS Therapy

The series of applications to which tDCS therapy can be applied are numerous. Whilst different applications of tDCS have been investigated with differing amounts of rigour, tDCS has been studied across multiple domains.

1. Mood Disorders: Numerous data support the notion that tDCS neuromodulation is able to produce antidepressant effects. Indeed, a 2016 meta-analysis of 6 clinical trials found it to produce dose-dependent effects in depressed patients. Furthermore, Flow Neuroscience recently released a pre-print describing a clinical trial using their device for the treatment of depression. Their study found 57% of participants to achieve full symptom remission after 10 weeks of treatment.

• Cognitive Enhancement: tDCS has shown promise in enhancing cognitive functions, particularly those involving the prefrontal cortex. Specifically, a 2023 meta-analysis found tDCS to improve working memory, response inhibition, cognitive flexibility and one’s ability to understand and attribute mental states to oneself and others. Interestingly, for some domains of function, these cognitive benefits appeared to be more robust when tDCS was applied to healthy adults compared to when it was applied to individuals with pre-existing cognitive dysfunction.

• Motor Rehabilitation: In neurorehabilitation settings, tDCS is used in individuals with motor dysfunction. It has oft been applied alongside physical therapy for the purpose of enhancing the rate of motor learning, as well as, potentially, the accuracy of movements during the physical therapy.

• Pain Management:  tDCS has been explored as a non-pharmacological approach for managing various types of pain, including chronic pain conditions such as fibromyalgia, neuropathic pain, and migraine.

• Other Psychiatric Disorders: Whilst tDCS has been the most robustly investigated as a potential treatment for depression, it may also have application in the treatment of other psychiatric disorders. These include anxiety, schizophrenia, and addiction. It may also help treat individual symptoms of such disorders, such as insomnia, appetite issues, high heart rate, pain and motor dysfunction.