Online, you can buy the headset below for $250. It promises to "overclock your brain" by "pass[ing] a small electric current (<2.05mA) through the prefrontal cortex of the wearer[,] making their synapses fire faster."

Other headsets sell for less than $60. They use transcranial direct current stimulation, or tDCS. It works by running a very low-voltage electrical current through your brain, strengthening its connections.

tDCS is "broadly considered safe for routine application even in healthy subjects." Withholding it from patients is often considered more dangerous than using it to help them. After over 50 thousand sessions of tDCS in clinical studies, no serious side effects have been reported.

The prefrontal cortex (PFC) is on the surface of the brain directly behind the forehead, making it one of the easiest brain areas to stimulate. As I described in part one of this series, increasing PFC neural activity can increase self-control and cognitive empathy. If tDCS devices can enhance the PFC and increase those capabilities, then they are a relatively cheap and easy tool for self-improvement.

A young but growing body of research has found that tDCS can reduce impulsivity and cravings for nicotine, alcohol and methamphetamines. It can increase caution, complex thought and performance on cognitive tasks including multitasking, and it may also be beneficial for learning.

In addition to enhancing working memory and self-control, it also might be an effective treatment for depression. It may even improve social skills. While the current method sometimes only provides temporary benefits, an advancement called transcranial Random Noise Stimulation provided a long-lasting benefit in learning math.

All of these benefits explain the rising popularity of tDCS devices. Even the U.S. military is using tDCS to help train drone pilots, for example, but the popularity of tDCS extends beyond official use. Many tDCS enthusiasts have purchased devices for personal use, and some have actually taken to constructing their own tDCS devices.

Before you rush out and buy a tDCS headset online, though (or make one yourself) it may help to know that researchers have sent out "a plea for extreme caution" about use by consumers.

The FDA is still figuring out regulations on the technology, since it could have negative effects if misused. For example, tDCS electrodes must be placed extremely precisely on the head; if placed incorrectly, they could alter the wrong brain regions. They must also have a specific polarity and voltage to be safe and effective.

Members of the tDCS community usually "draw heavily on scientific knowledge" while applying the technology, but that is not enough to rely on to ensure safe consumer use.

Still, even without regulations, tDCS can be widely implemented for medical purposes because of it is used in a systematic and controlled way by trained professionals.

Once the appropriate regulations are in place, though, tDCS opens up huge opportunities for psychiatric treatment and personal growth. It can be used not only to treat mental illnesses, but to increase individual self-control and potential among those who are "normal" as well.

The most exciting part of tDCS is not the benefits that it can offer right now, but what it means for the future. Too much of the human mind has been outside of our control throughout history, but the development of new neurotechnology can give us control of ourselves so that we are no longer slaves to nature.

For more information on this subject, check out some of the following resources:

Nature: "Your Electric Pharmacy"

Slate: "Spark of Genius"

ABC: "New directions for brain research"

The New Yorker: "Electrified: Adventures in transcranial direct-current stimulation"