Electric and magnetic fields have been gaining ground as brain therapies because they can exert force on charged objects, such as neurons. Yet they typically affect cells indiscriminately, including healthy ones. Now researchers are looking to aim the fields more precisely to treat brain cancer and major depression.

In 2011 the U.S. Food and Drug Administration approved a portable cap that delivers low-intensity, alternating electric fields to tumors in adults with recurrent glioblastoma multiforme, the most common and stubborn form of brain cancer. Rapidly dividing cancer cells have a unique electrical charge and shape, which allows the electric fields to single them out. By dismantling cell-copying machinery, the fields ultimately goad tumor cells into suicide. The technology is now being tested on other types of tumors, including those that appear in meningioma (cancer of the brain's lining) and lung cancer.

Another emerging technique also seeks to hit only desired targets, this time to treat major depression. Still highly experimental, magnetic seizure therapy (MST) showers certain brain areas with strong, rapidly alternating magnetic fields, provoking chemical changes in neurons that cause them to fire simultaneously and induce a seizure. The goal is the same as with electroconvulsive therapy (ECT), colloquially known as shock therapy; for unknown reasons, sparking electrical activity in the cortex relieves symptoms of depression. ECT, however, hits a larger swath of tissue and may cause memory loss and other bad side effects as the seizures spread through the brain. Researchers hope the more localized MST will one day replace ECT.