If you follow neuroscience and neuroengineering, it’s hard to ignore the offerings of cutting-edge research seeming to reanimate an antediluvian procedure of pelting the brain with electricity. Today’s more modern and civilized brain zapping is less invasive, more controlled and uses various levels of direct and alternating electrical currents to repair and augment a panoply of different cognitive functions. Results range from relieving severe, treatment-resistant depression, jumpstarting vocabulary recall, enhancing math skills, boosting self-control, fortifying the aging brain as well as reducing the intention to commit violent acts and sexual assault. The scientific literature fosters an impression of our most complex organ’s thirst for precisely tailored doses of electrically charged particles with the long-term effects still unknown. Adding to the literature, today the United States Department of Defense published its findings in JNeurosci based on a small, preliminary study showing transcranial electric stimulation enhanced consolidation of recent experiences into long-term memories while subjects were bedded down in uninterrupted slumber.

The project, funded by United States Defense Advanced Research Projects Agency (DARPA), recruited 16 healthy adult participants. Before bed, the subjects were presented with still images of complex visual scenes. They were trained to identify targets like snipers, suicide bombers and explosive devices disguised as dead animals, fruit, flora and detritus. Subjects spent three non-consecutive nights in a sleep lab with a cap made of electrodes placed on their heads. After drifting off they were administered closed-loop slow-wave transcranial alternating current stimulation (tACS).

Learning (long-term memory consolidation) is a two-tiered process. In the hours immediately following the acquisition of new information, new learning marinates in your short-term memory (synaptic consolidation). The process of encoding short-term memories into long-term memories (system consolidation) takes considerably more time and sleep plays an important role. While you sleep, your brain amps up the process of memory consolidation. Brain activity spikes naturally during sleep. Researches applied a parallel closed-loop slow-wave tACS brain stimulation hoping the confluence of naturally occuring and externally administed energy would precipitate long-term memory storage.

When subjects had their brains stimulated during sleep, they later demonstrated improved performance in detecting targets in new visual scenes, compared with their performance after nights where they did not receive tACS. The results suggest a consolidation of new experience into long-term memory is enhanced by closed-loop slow-wave tACS, and that the electrical stimulation can be administered without disrupting sleep.

tACS and other forms of electrical brain stimulation are hitting the mainstream as a novel, non-pharmaceutical way to bypass the blood-brain barrier, shore up the intellect, stabilize mood and treat a number of debilitating conditions. So what kinds of electrical brain stimulation technologies are currently in therapeutic rotation?

Types of electrical brain stimulation. Effects, knowns and unknowns:

tCS: Transcranial Current Brain Stimulation is an umbrella term for a group of noninvasive electrical brain stimulation techniques. ‘Transcranial’ means passing through the cranium.

TMS: Transcranial Magnetic Stimulation is a noninvasive technique. A device is placed on the scalp that uses magnetic fields to excite brain cells. TMS has gained attention for treating severe depression.

rTMS: Repetitive Transcranial Magnetic Stimulation (repetitive treatments of TMS) is used to treat severe depression, anxiety, migraines, psychosis and chronic pain. Mayo Clinic reports minimal side effects for both TMS and rTMS, with some reports of more serious and rare side effects, including seizure and hearing loss if the patient isn’t wearing hearing protection during the procedure. More studies are needed to evaluate long-term effects.

tDCS: Transcranial Direct Current Stimulation was initially developed to treat depression and brain injuries. It is noninvasive with minimal to zero discomfort reported. Studies show it also augments learning including language, math and motor skills. The latest research suggests it produces less violent, more salubrious intentions in the average adult. Consumer tDCS devices are available to the public for purchase and DIY application. Long-term effects are still unknown.

tRNS: Transcranial Random Noise Stimulation zaps the brain with random frequency and amplitude increasing gamma oscillation in the auditory cortex. It’s used to treat pain associated with fibromyalgia and it’s still not completely understood how it works. Some evidence suggests it enhances cognitive training and math skills. Long-term effects are yet to be seen.

tACS: Transcranial Alternating Current Stimulation (tACS) is a noninvasive, low-level alternating current applied to the cranium. New research out today suggests it expedites memory consolidation while you sleep. As with the above noninvasive transcranial stimulation techniques, it is not fully understood how it works and the long-term effects are unknown.

ECT: Electroconvulsive Therapy (ECT) more commonly known as Electroshock Therapy, is the earliest form of electric brain stimulation and one of the most controversial, casting a long shadow on modern day techniques. Invented in Italy in 1938, it used to be administered without anesthetic and caused serious side effects including bone fractures and memory loss. Today, patients are placed under anesthesia while an electrical current is used to induce a seizure for therapeutic benefit. ECT is most often reserved as a last resort for patients with suicidal depression as well as mania or catatonia. Reported side effects can include physical discomfort and memory loss. This therapy was featured in the Showtime series “Homeland” as a means of treating the character Carrie Mathison’s bipolar disorder.

DBS: Deep Brain Stimulation is an invasive technique that requires brain surgery. DBS is a treatment option for depression, obsessive compulsive disorder (OCD), and Parkinson’s disease. Risks are significant and include stroke. This is a relatively new procedure and long-term effects have yet to be evaluated.

The brain is capable of so many incredible things that any noninvasive technique with the potential for enhancement carries a far-reaching and alluring promise. But with both invasive and noninvasive electric brain stimulation, many aspects of the technology’s effectiveness are not well understood and the long-term effects are still unknown.