Is it safe? Obviously the test wasn’t designed to assess any possible negative cognitive effects, but apart from some, “skin tingling, itching, and mild burning sensations” the subjects tolerated frequent TES (transcranial electric stimulation) well.
In the present study, we tested the tolerability (safety) and compliance, compared to sham, of two common tES approaches having a current density < 2 mA/cm2; transcranial Direct Current Stimulation (tDCS) or transcranial Pulsed Current Stimulation (tPCS) used by healthy subjects three to five days (17 – 20 minutes per day) per week for up to six weeks in a naturalistic environment. In this study 100 healthy subjects were randomized to one of three treatment groups: tDCS (n = 33), tPCS (n = 30), or sham (n = 37) and blinded to the treatment condition. The tES and sham waveforms were delivered through self-adhering electrodes on the right lateral forehead and back of the neck. We conducted 1905 treatment sessions (636 sham, 623 tDCS, and 646 tPCS sessions) on study volunteers over a six-week period. There were no serious adverse events in any treatment condition.
This comes to us via the Neuroelectrics.com blog. I’m very excited to see Neuroelectrics on the scene. I first noticed their device Starstim (pictured), popping up in news around Roi Cohen Kadish’s ongoing tDCS trials at his Oxford lab (see). I believe Neuroelectrics is a Spanish company. What’s especially exciting to me is that they also make an EEG device called Enobio and are working on the ability to map brain activity with EEG while undergoing tDCS. Think about that! Live, in-the-moment feedback on exactly what effect your tDCS is having.
More than 100 studies have been performed using tDCS in healthy controls and in patient populations, and no serious side effects have occurred for a review, see Nitsche and others 2008. Slight itching under the electrode, headache, fatigue, and nausea have been described in a minority of cases in a series of more than 550 subjects Poreisz and others 2007. Detailed studies have been performed to assess the safety of tDCS. These have shown that there was no evidence of neuronal damage as assessed by serum neuron-specific enolase after application of a 1 mA anodal current for 13 minutes Nitsche and Paulus 2001; Nitsche, Nitsche, and others 2003 or MRI measures of edema using contrast-enhanced and diffusion-weighted MRI measures after application of a 1 mA current for 13 minutes anodal or 9 minutes cathodal; Nitsche, Niehaus, and others 2004 […] In addition, a recent study was performed in rats using an epicranial electrode montage designed to be similar to that used in tDCS Liebetanz and others 2009. This demonstrated that brain lesions occurred only at current densities greater than 1429 mA/cm2 applied for durations longer than 10 minutes. In standard tDCS protocols in humans, a current density of approximately 0.05 mA/cm2 is produced.
Safety of the method
Several studies have been performed on the safety of tDCS and on side effects and have resulted in clear recommendations on its safe use. There is general agreement that if attention is paid to recommendations concerning contraindications and stimulation parameters, tDCS is a well tolerated method with minimal side effects Nitsche et al. 2003, Fregni et al. 2006, Iyer et al. 2005.
The physiological changes involve the modulation of spontaneous neuronal activity through polarity-specific shifts of the resting membrane potential in the direction of de- or hyperpolarisation. The direction of the change is governed by the direction of current flow, the spatial orientation of the neuron, the type of neuron and the total charge. This underlies the possible complication of inducing an epileptic seizure. In accordance with the safety protocol from Nitsche and Paulus 2000, the stimulation charges used here lie far below the charges necessary to trigger a seizure. Even a continuous stimulation just below the energy threshold for triggering a seizure was associated with only a 40% increased cortical excitability compared with baseline. Studies on the question of whether neuronal damage can be observed after tDCS and whether structural changes occur in the brain revealed no indications of damaging effects of tDCS. Thus, levels of neuron-specific enolase NSE, a marker for neuronal destruction, were not increased after tDCS Nitsche et al. 2003 and pathological changes could not be found in either contrast-enhanced MRT or in EEG Nitsche 2003.
Persistent disorders of motor and cognitive abilities have not been found. Electrically induced local muscle contractions during the stimulation can be unpleasant for the person undergoing tDCS. The electrical stimulation causes irritation of the scalp lasting just a few seconds, which has been described as more or less painful tingling and pulling Fregni et al. 2006. Cortical tissue damage has not been found, even after high stimulation intensities and frequencies. Stimulation with electrodes on the scalp could indeed result in a chemical reaction and in burning of the skin tissue. However, the risk of a skin burn is minimised if sponge electrodes soaked in salt water are used, in accordance with the safety protocol of Nitsche and Paulus 2000.
Fregni et al. did not describe any side effects in their studies Bip Disorders 2006, Clin Neurophysiol 2006, Depr and Anx 2006; the treatment was well tolerated by all the patients.