A Harvard Medical School study published in the Neuroscientist highlights the potential of portable medical devices that treat depression, anxiety, and insomnia. The Fisher Wallace Cranial Stimulator, one of the devices mentioned in the study, has been on the market since 1991. According to its manufacturer, the device generates microcurrents of electricity to stimulate the brain's production of serotonin and dopamine. A prescription is required for the device, which can be used at home on a daily basis.

The Harvard study concludes that use of cranial electrical stimulation in humans has so far resulted in few adverse effects. And, although the study cautions that more research is needed, it says that preliminary studies of the method "show promising results and should be explored further."