The basics of HD-tDCS
High-Definition transcranial Direct Current Stimulation, or HD-tDCS for short, is a form of tDCS where current is applied through small electrodes. As opposed to the large sponge pad electrodes used in regular TDCS. The small electrodes are called High-Definition electrodes, or HD-Electrodes, hence the overall name. HD + tDCS. HD electrodes are small cups filled with gel as shown in this video:Technique and Considerations in the Use of 4×1 Ring High-definition Transcranial Direct Current Stimulation (HD-tDCS)
Just like with tDCS where there is the M1-SO montage or the bifrontal montage (see our placement guide here) with HD-tDCS you can place the electrodes in different ways. But with HD-tDCS you can also select the number of electrodes. HD-tDCS is commonly done with 5 electrodes (using the 4×1 montage), but can be done with as little as two electrodes, or with dozens of electrodes at once. What all these approaches share is using HD electrodes.
You always need HD electrodes and an HD cap to hold the electrodes in place. The HD electrodes are prepped with HD gel and then an HD circular electrode is inserted in the gel and cup, and connected to the stimulator. Now how many channels of HD you can do will depend on your stimulator. If you got a basic tDCS stimulator (see the guide here) then you are limited to two HD electrodes. The 4×1 HD adaptor converts a basic stimulator into one capable of 5 electrode 4×1 HD-tDCS. And if you got the resources and access, the “MxN” stimulators give you all the channels.
Why do HD-tDCS?
Given all the uses for regular tDCS, the question is why use HD-tDCS? According to Marom Bikson who co-invented HD-tDCS, it depends on your goals. If its ok to stimulate a larger section of brain with “circuit therapeutics” then regular tDCS works great. But if the goal is to stimulate just one part of the brain then HD-tDCS is the way to go.
Does HD-tDCS work as clinical treatment?
As far as trials of HD-tDCS treatment, here is a partial selection
- Depression in elderly
- Sleep in older adults
- Memory in older adults
- Children with disorders of consciousness
- Physical Endurance
- Physical Performance – Reference 1 – Reference 2 – Reference 3
- Tinnitus link – Reference 1 – Reference 2 – Reference 3 – Reference 4
- Pediatric Epilepsy
- Obsessive-compulsive disorder (OCD)
- Cognition in older adults
- Aphasia (stroke) – Reference 1 – Reference 2
- Facial pain
- Motor learning in children – Reference 1 – Reference 2
- Motor function after Stroke
- Auditory hallucinations in dementia
- Auditory hallucinations in schizophrenia – Reference 1 – Reference 2
- Impulsivity – Reference 1 – Reference 2
- Fibromyalgia pain – Reference 1 – Reference 2
- Temporomandibular disorders (TMD) pain