Transcranial Direct Current Stimulation (tDCS) vs Transcranial Alternating Current Stimulation (tACS)

What are the Advantages/Disadvantages of tDCS and tACS

You might be wondering what the difference between AC and DC Transcranial
Current Stimulation is. In short, tDCS and tACS have different stimulation
paradigms. From the diagram below, you can see that direct current will
typically be switched on for several minutes, while tACS uses alternating
currents for either rectangular (dotted line) or sinusoidal (solid line)
stimulation.

Advantages:

tDCS
  • Modulates spontaneous neuronal activity in polarity dependent fashion
  • Site-specific effects that are perpetuated throughout the brain
  • Significant effects on high order cortical processes like decision making, memory, language, sensory perception, pain
  • Useful in emotional regulation and visuospatial attention – up- and down regulation of different brain regions
  • Small currents that do not evoke action potentials
  • Extremely promising in treating depression
tACS
  • May offer novel method to improve subjective sleep quality after a night with poor sleep
  • Allows for modulation of brain oscillations
  • Causally link brain oscillations of a specific frequency range to cognitive processes
  • If specific frequencies associated with a cognitive function are known, tACS can be applied at that exact frequency.
  • Modulate basic motor and sensory processes as well as higher cognitive processes like memory, ambiguous perception, decision making
  • Helpful for increasing sleep quality and efficiency in healthy people and people with sleep disorders
  • Direction insensitivity of stimulation
  • Higher skin perception threshold during stimulation

Disadvantages:

tDCS
  • Low spatial resolution
  • High potential for placebo effect
  • Hard to define localization of the electrodes
  • Large variability in effects between individuals
  • Factors to do with hormones and fatigue levels likely to interact with tDCS
  • Enhancing mental function in one area can negatively impact another
tACS
  • Does not have a conventional cathode so up- and downregulation of different brain regions is not well-understood
  • Experiments that require inhibition of particular brain regions are out of reach
  • Lack of electrophysiological evidence
  • Intracranial current density varies between people

tDCS as the most prevalent method

tDCS is the more prevalent method between tDCS and tACS. Although it is
still considered an ‘experimental’ form of brain stimulation just like tACS, it
has been well-researched as valuable for the treatment of a variety of
neuropsychiatric conditions. Some tDCS brands on the market include
Caputron, BrainDriver, Apex, and Focus Go, who have developed tDCS
devices widely used today in clinical settings and by individuals worldwide.

Which do I prefer?

Due to the fact that much more research has been done on tDCS devices and
it has become widespread in the market, tDCS devices seem to be more
reputable. Stimulation with direct current has shown to be valuable when
looking at the effects of cortical modulation on networks in the brain, having
site-specific effects. These significant effects on high-order cortical processes
in sensory perception, pain, language, memory, and more prove more
valuable and notable than AC stimulation’s modest effects on cortical excitability.
However, there are definitely opportunities for cranial AC stimulation to
emerge as one of the new options in brain stimulation therapy. Studies have
shown that motor evoked potentials (action potential elicited by noninvasive
stimulation) are significantly increased with tACS but not tDCS and the mean
stimulation effect is higher with tACS. They have many similarities in that
tACS can also treat high order cortical processes and neuropsychiatric
conditions, however, tDCS devices are already well-established and has
much less skepticism surrounding it.

Fisher Wallace

Fisher Wallace has emerged as the most well-known brand to market FDA
cleared tACS devices. While the market is saturated with tDCS devices,
Fisher Wallace chooses to use alternating current over direct current, where
the flow of electrons frequently change direction. The Fisher Wallace tACS
device is a wearable brain stimulation device working to treat symptoms of
insomnia, anxiety, and depression through stimulation of serotonin
production and alpha wave production, while lowering the stress hormone
cortisol. From the comfort of the individual’s home, patients can experience
long-lasting symptom relief within the first week of use.