Imagine if your biggest health problem could be solved with the flip of a switch. Deep-brain stimulation (DBS) offers such a dramatic recovery for a range of neurological illnesses, including Parkinson's disease, epilepsy and major depression. Yet the metal electrodes implanted in the brain are too bulky to tap into intricate neural circuitry with precision and corrode in contact with tissue, so their performance degrades over time. Now neurophysiologists have developed a method of DBS that avoids these problems by using microscopic magnets to stimulate neurons.
In experiments published in June 2012 in Nature Communications, neurophysiologist John T. Gale of the Cleveland Clinic and his colleague Giorgio Bonmassar, a physicist at Harvard Medical School and an expert on brain imaging, tested whether micromagnets (which are half a millimeter in diameter) could induce neurons from rabbit retinas to fire. They found that when they electrically energized a micromagnet positioned next to a neuron, it fired.
In contrast to the electric currents induced by DBS, which excite neurons in all directions, magnetic fields follow organized pathways from pole to pole, like the magnetic field that surrounds the earth. The researchers found that they could direct the stimulus precisely to individual neurons, and even to particular areas of a neuron, by orienting the magnetic coil appropriately. “That may help us avoid the side effects we see in DBS,” Gale says, referring to, for instance, the intense negative emotions that are sometimes accidentally triggered when DBS is used to relieve motor problems in Parkinson's.
The micromagnets also solve other problems associated with metal electrodes. The magnetic field easily penetrates the magnets' plastic coating, which prevents corrosion and the ensuing inflammation of brain tissue. “I've been doing DBS research for 14 years now, and this is a totally different way of thinking about activating the brain for me, which is very exciting,” Gale says.
Although the study focused on stimulating neurons, micromagnets could be used to activate other excitable tissues, such as in the heart, inner ear or muscles in our extremities, as part of a pacemaker or prosthetic device. In humans, the micromagnets would be turned on and off by an external control pack, either wirelessly or by connecting to a wire implanted under the skin. A medical company has acquired the rights to manufacture the micromagnets, and if animal research continues to show them to be safe and effective, these devices could be tested in humans within five years, according to Gale.