The Clinical Uses of tDCS: Depression

Transcranial Direct Current Stimulation (tDCS) is a type of neurostimulation where you apply a very small level of direct current (commonly 1mA - 2mA) through one electrode (Anode) and it flows through the brain to another electrode (Cathode). The direct current then creates a condition under the electrode that affects the neurons: the basement membrane of the neurons at the anode become more positive making them more likely to fire, and the basement membrane of the neurons at the cathode become more negative making them less likely to fire.   

This has led research to experiment with different arrangements of electrodes (called montages) to encourage activity at the anode, and lower activity at the cathode; the cathode is sometimes used away from the head purely as current return and no neurophysiological activity. The amount of research using tDCS is substantial and has been growing steadily over the past ten years (see graph below).

A few months ago, I did a short review of the main topics of tDCS research:

Hits on Pubmed

tDCS and Learning                         322
tDCS and Stroke                             288
tDCS and Memory                          214
tDCS and Depression                     208
tDCS and Pain                                162
tDCS and Safety                             108
tDCS and Cognitive Enhancement  55
tDCS and Bipolar                           31
tDCS and Parkinson's                     25
tDCS and Alzheimer's                    13

Considering the clinical uses of tDCS, not surprisingly it is limited to neurological disorders. As you can imagine with the type of growth seen in the graph of the number of tdcs studies published by year, that topics of tdcs research is growing wider and deeper. That is there are more conditions that are investigated, and with a few conditions, more studies are made. The top clinical conditions used for tDCS are depression, stroke, and pain.

The use of tDCS in the clinical environment is still in its infancy. Mostly not used in general practice,  tDCS is still the realm of Brain Stimulation Centers throughout the US; practices that specialize in brain stimulation techniques. Hopefully this changes over the next few years, as tDCS devices are so easy to acquire, tDCS techniques are so easy to implement, and the side effects are minimal, the technology is ready for growth. Because of lack of clinical precedent, it is key to look into the research to understand protocols.

Below I will highlight a little of the research and give the summary for general interest.

Depression

1. Boggio PS, Rigonatti SP, Ribeiro RB, Myczkowski MI, Nitsche MA, et al. A randomized, double-blind clinical trial on the efficacy of cortical direct current stimulation for the treatment of major depression. Intl J of Neuropsychopharma 2008;11:249-254.





"The results of this study show that cortical stimulation
with tDCS is associated with a significant reduction in
depression scores that is specific to the site of stimulation
and lasts for at least 30 d after the end of treatment."

Successful Montage: Anode L DorsoLateral PreFrontal Cortex (DLPFC), and Cathode R Supraorbital

Level: 2mA


Length: 20min per day for 10 days






2. Loo CK, Alonzo A, Martin D, Mitchell PB, Galvez V, et al. Transcranial direct current stimulation for depression: 3 week randomized, sham controlled trial. British J of Psychiatry 2012;200:52-59.

"Although results after 3 weeks of daily tDCS were modest, the
number of responders after 6 weeks of treatment was much more
encouraging, and comparable with outcomes from a recent large
study of 6 weeks of TMS given on an open-label basis to
participants with pharmacotherapy-resistant depression.
The response rate was superior to that reported
for antidepressant medication in individuals who had failed a first
course of medication in the large Sequenced Treatment
Alternatives to Relieve Depression (STAR*D) study.
This suggests that tDCS has meaningful antidepressant efficacy,
including in those individuals resistant to pharmacotherapy."


Successful Montage: Anode L DorsoLateral PreFrontal Cortex (DLPFC), and Cathode R Lateral Orbit (F8)

Level: 2mA


Length: Every day for three weeks then once per week for three more weeks.




3. Martin DM, Alonzo A, Ho Ka, Player MK, Mitchell PB, et al. Continuation of transcranial direct current stimulation for the prevention of relapse in major depression. J Affective Disorders 2012;144:274-278.

"Continuation tDCS,given weekly for the first 3 months,
resulted in the majority of responders remaining well, though
the relapse rate increased after treatments were spaced to fort-
nightly in the subsequent 3 months.In the absence of a control
group of responders who did not go on to receive continuation
tDCS treatments,we cannot conclude that the continuation
treatments were beneficial in preventing relapse,though the
higher rate of relapse when treatments were spaced to fortnightly
suggests that the weekly treatment schedule may be a useful
treatment strategy."

Successful Montage: Anode L DorsoLateral PreFrontal Cortex (DLPFC), and some with Cathode R Lateral Orbit (F8) and some with Cathode R upper shoulder

Level: 2mA


Length: Weekly for the first three months then every other week for three months after that.
Even though all three studies listed above have Anode L DLPFC, this is most definitely not the only montage used for depression and tDCS; but it is a well known choice.

I want to follow up with a later blog for research highlight of tDCS use for Stroke and Pain.