Watching individual neurons respond to magnetic therapy

June 29, 2014, Duke University
The light grey coil on the left is a conventional, commercially available TMS coil. The black coil on the right is the new, innovative version designed to fit a smaller non-human primate's cranium and work with the neural monitoring device. Credit: Warren Grill

Engineers and neuroscientists at Duke University have developed a method to measure the response of an individual neuron to transcranial magnetic stimulation (TMS) of the brain. The advance will help researchers understand the underlying physiological effects of TMS—a procedure used to treat psychiatric disorders—and optimize its use as a therapeutic treatment.

TMS uses magnetic fields created by electric currents running through a wire coil to induce neural activity in the brain. With the flip of a switch, researchers can cause a hand to move or influence behavior. The technique has long been used in conjunction with other treatments in the hopes of improving treatment for conditions including depression and substance abuse.

While studies have demonstrated the efficacy of TMS, the technique's physiological mechanisms have long been lost in a "black box." Researchers know what goes into the treatment and the results that come out, but do not understand what's happening in between.

Part of the reason for this mystery lies in the difficulty of measuring neural responses during the procedure; the comparatively tiny activity of a single neuron is lost in the tidal wave of current being generated by TMS. But the new study demonstrates a way to remove the proverbial haystack.

The results were published online June 29 in Nature Neuroscience.

"Nobody really knows what TMS is doing inside the brain, and given that lack of information, it has been very hard to interpret the outcomes of studies or to make therapies more effective," said Warren Grill, professor of biomedical engineering, electrical and computer engineering, and neurobiology at Duke. "We set out to try to understand what's happening inside that black box by recording activity from single neurons during the delivery of TMS in a non-human primate. Conceptually, it was a very simple goal. But technically, it turned out to be very challenging."

The interdisciplinary team that developed the method to record an individual neuron's response during transcranial magnetic stimulation. Clockwise from top left: Michael Platt, director of the Duke Institute for Brain Science, Center for Cognitive Neuroscience; Warren Grill, professor of biomedical engineering, electrical and computer engineering, and neurobiology; Marc Sommer, associate professor of biomedical engineering and neurobiology; and Tobias Egner, assistant professor of psychology and neuroscience. Credit: Duke University

First, Grill and his colleagues in the Duke Institute for Brain Sciences (DIBS) engineered new hardware that could separate the TMS current from the neural response, which is thousands of times smaller. Once that was achieved, however, they discovered that their recording instrument was doing more than simply recording.

The TMS magnetic field was creating an through the electrode measuring the neuron, raising the possibility that this current, instead of the TMS, was causing the . The team had to characterize this current and make it small enough to ignore.

Finally, the researchers had to account for vibrations caused by the large current passing through the TMS device's small coil of wire—a design problem in and of itself, because the typical TMS coil is too large for a non-human primate's head. Because the coil is physically connected to the skull, the vibration was jostling the measurement electrode.

The researchers were able to compensate for each artifact, however, and see for the first time into the black box of TMS. They successfully recorded the action potentials of an individual neuron moments after TMS pulses and observed changes in its activity that significantly differed from activity following placebo treatments.

Grill worked with Angel Peterchev, assistant professor in psychiatry and behavioral science, biomedical engineering, and electrical and computer engineering, on the design of the coil. The team also included Michael Platt, director of DIBS and professor of neurobiology, and Mark Sommer, a professor of .

They demonstrated that the technique could be recreated in different labs. "So, any modern lab working with non-human primates and electrophysiology can use this same approach in their studies," said Grill.

The researchers hope that many others will take their method and use it to reveal the effects TMS has on neurons. Once a basic understanding is gained of how TMS interacts with neurons on an individual scale, its effects could be amplified and the therapeutic benefits of TMS increased.

"Studies with TMS have all been empirical," said Grill. "You could look at the effects and change the coil, frequency, duration or many other variables. Now we can begin to understand the of TMS and carefully craft protocols rather than relying on trial and error. I think that is where the real power of this research is going to come from."

Explore further: Magnetic fields prevent editor from talking (w/ video)

More information: "Simultaneous transcranial magnetic stimulation and single neuron recording in alert non-human primates." Mueller, J.K., Grigsby, E.M., Prevosto, V., Petraglia III, F.W., Rao, H., Deng, Z., Peterchev, A.V., Sommer, M.A., Egner, T., Platt, M.L., Grill, W.M. Nature Neuroscience, June 29, 2014. DOI: 10.1038/nn.3751

Related Stories

Magnetic fields prevent editor from talking (w/ video)

April 12, 2011
(PhysOrg.com) -- By holding an electromagnet close to a person’s skull, researchers can alter the neuron activity in the person’s brain. This technique, called transcranial magnetic stimulation (TMS), can be used ...

Magnetic therapy becoming more popular for treating depression

February 6, 2012
(Medical Xpress) -- A new magnetic therapy that treats major depression recently received a major boost when the government announced Medicare will cover the procedure in Illinois.

New research confirms efficacy of transcranial magnetic stimulation for depression

July 26, 2012
In one of the first studies to look at transcranial magnetic stimulation (TMS) in real-world clinical practice settings, researchers at Butler Hospital, along with colleagues across the U.S., confirmed that TMS is an effective ...

Magnetic treatment improves stroke patients' ability to communicate

November 15, 2011
(Medical Xpress) -- Magnetic stimulation of the brain could help improve language skills of stroke survivors with aphasia, according to research by The University of Queensland.

New treatment welcome news for Parkinson's and stroke patients

July 11, 2012
(Medical Xpress) -- New research developed by The University of Queensland is set to change the future treatment of speech problems associated with stroke and Parkinson's disease.

Recommended for you

Brain zaps may help curb tics of Tourette syndrome

January 16, 2018
Electric zaps can help rewire the brains of Tourette syndrome patients, effectively reducing their uncontrollable vocal and motor tics, a new study shows.

A 'touching sight': How babies' brains process touch builds foundations for learning

January 16, 2018
Touch is the first of the five senses to develop, yet scientists know far less about the baby's brain response to touch than to, say, the sight of mom's face, or the sound of her voice.

Researchers identify protein involved in cocaine addiction

January 16, 2018
Mount Sinai researchers have identified a protein produced by the immune system—granulocyte-colony stimulating factor (G-CSF)—that could be responsible for the development of cocaine addiction.

Neuroscientists suggest a model for how we gain volitional control of what we hold in our minds

January 16, 2018
Working memory is a sort of "mental sketchpad" that allows you to accomplish everyday tasks such as calling in your hungry family's takeout order and finding the bathroom you were just told "will be the third door on the ...

Brain imaging predicts language learning in deaf children

January 15, 2018
In a new international collaborative study between The Chinese University of Hong Kong and Ann & Robert H. Lurie Children's Hospital of Chicago, researchers created a machine learning algorithm that uses brain scans to predict ...

Preterm babies may suffer setbacks in auditory brain development, speech

January 15, 2018
Preterm babies born early in the third trimester of pregnancy are likely to experience delays in the development of the auditory cortex, a brain region essential to hearing and understanding sound, a new study reveals. Such ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.