For dozens of years, researchers and doctors have been looking for ways to influence brain activity without opening the skull, so as to conduct fundamental brain research in human beings and treat brain disorders. Brain stimulation has already helped patients with symptoms of depression, and the technique is also increasingly popular for dementia, chronic pain, and epilepsy. When the brain activity in specific areas is too high, for instance, it may be interesting to temporarily reduce it.
Existing methods include electrical stimulation, sound waves, and infra-red light, but the most commonly used technique is Transcranial Magnetic Stimulation (TMS). TMS involves producing a magnetic field in a coil that is placed on the skull. This magnetic field generates an electric current in the brain, to which the brain cells react.
However, after almost thirty years of research, the precise effect of TMS on the brain cells and the size of the activated area in the brain still remained unknown.
That’s why Maria Romero and her colleagues from the Department of Neurosciences at KU Leuven examined how the brain of rhesus monkeys – which strongly resembles the human brain – responds to TMS. The researchers placed a micro-electrode in the brain area underneath the TMS coil. This allowed them to measure how the brain cells responded to impulses from the coil. They were also able to determine the size of the area in which the brain activity changed as a result of TMS.
“The electrical activity in most brain cells strongly increased for less than a tenth of a second after the TMS pulse,” researcher Maria Romero explains. “Contrary to what the computer models had predicted, the activated area in the brain turned out to be very small (red in the figure): approximately 2 millimetres by 2 millimetres. This may explain why brain stimulation treatments have varying degrees of success in patients.”
In the future, measuring the effect of different methods of brain stimulation directly in the brain cells may allow researchers to find more targeted and safer ways to stimulate our brains. Non-invasive brain stimulation, for instance, might help improve our memory or the quality of our sleep.