27 September 2007

Transcranial Magnetic Stimulation--For Targeted Neural Suppression

Transcranial Magnetic Stimulation (TMS) is a noninvasive way to stimulate neural activity using noninvasive electromagnetic coil devices placed over specific areas of the scalp. TMS has been used to treat depression, schizophrenia, and to rehabilitate from stroke (CVA).

Recent research suggests that TMS might also be used to selectively suppress specific regions of the brain, for research and possibly for therapy.
In a set of experiments, the researchers used TMS to generate weak, electrical currents in the brain with quick 2- to 4-second bursts of magnetic pulses to the visual cortex of cats. Direct measurements of the electrical discharge of nerve cells in the region in response to the pulses revealed that TMS predictably caused an initial flurry of neural activity, significantly increasing cell firing rates. This increased activity lasted 30 to 60 seconds, followed by a relatively lengthy 5 to 10 minutes of decreased activity.

What the researchers were able to determine for the first time was that the neural response to TMS correlated directly to changes in blood flow to the region. Using oxygen sensors and optical imaging, the researchers found that an initial increase in blood flow was followed by a longer period of decreased activity after the magnetic pulses were applied.

"This long-lasting suppression of activity was surprising," said Brian Pasley, a graduate student at HWNI and co-lead author of the study. "We're still trying to understand the physiological mechanisms underlying this effect, but it has implications for how TMS could be used in clinical applications."

The critical confirmation of the connection between blood flow and neural activity means that researchers can use TMS to alter neural activity, and then use fMRI, which tracks blood flow changes, to assess how the nerve cells respond over time.

"One of the most exciting applications of TMS is the ability to non-invasively modify neural activity in specific ways," said Pasley. "The brain is malleable, so brain stimulation may be used to alter and promote specific functions, like learning and memory, or suppress abnormal activity that underlies neurological disorders. If we can figure out the right ways to stimulate the brain, TMS will likely be useful in attempts to improve neural function."

Initially, this use of TMS will probably be used by researchers with animals, to test its potency and safety. But neurologists are desperately looking for good tools to rehabilitate stroke patients and patients with neurodegenerative disorders.

The combination of TMS with neurofeedback should be a particularly potent tool for neurologists and psychiatrists who are just a bit bolder than most of their colleagues.


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