Brain Primer

Activating Brain Circuits with Transcranial Simulation

  • Reviewed18 Sep 2023
  • Author Knvul Sheikh
  • Source BrainFacts/SfN
Man getting a transcranial stimulation via Image Source Trading Ltd

Neurons in our brain typically communicate through electrical and chemical signals within the brain. Researchers have used pulses of magnetic fields and electrical currents over the outside of the skull to generate weak electrical currents in brain tissue, activating neurons, in hopes of treating diseases and disorders.

A few noninvasive treatments can stimulate cells near the surface of the brain: transcranial magnetic stimulation (TMS) and transcranial electrical stimulation techniques like transcranial direct current stimulation (tDCS) or transcranial alternating current stimulation (tACS). All of these treatments use magnetic fields or low electrical currents to alter neural activity in a specific region of the human cortex and, indirectly, deeper brain structures to which it connects.

During TMS therapy, people sit in a chair while a nurse or technician places a magnetic stimulator against their head. The device painlessly delivers brief magnetic pulses to the brain, similar in strength to those generated by magnetic resonance imaging (MRI) devices, but highly targeted. For people with depression, pulses are focused over their left prefrontal cortex. Here, they generate electrical currents among neurons, which over time adjust neural circuits, and may help change the person’s mood.

Similarly, tDCS uses one or two one thousandths of an Amp (or one to two milliamperes) of direct current to tune the brain. Although research into tDCS and its close cousin, tACS, is in its early stages, these techniques offer clear advantages over deep brain stimulation and even over TMS. Generally, people report only a slight tingling or tapping feeling on their head as the therapy is administered. The devices used to administer these therapies are also cheaper, more portable, and lower tech compared to TMS.

The U.S. FDA has approved the use of TMS devices for depression and obsessive-compulsive disorders. Meanwhile, tDCS is not FDA-approved but is sometimes used in treatment for major depressive disorder in areas like the European Union, Australia, and Mexico. Currently, there is no consensus among scientists on the mechanisms for how these treatments work, the best way to position the stimulation devices, or the right frequency and length of stimulation on a particular brain region for a given treatment. 

Adapted from the 8th edition of Brain Facts by Knvul Sheikh.



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