Motor Network Stimulation Shows Promise for Modulating Motor Excitability

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WASHINGTON — Compared with the primary motor cortex alone, stimulating the motor network was more efficacious in modulating motor excitability over time, according to study findings.

“Although the data are preliminary, what they show is that it's possible to stimulate a brain network instead of stimulating particular regions in isolation, and that stimulating a network could potentially be even more effective,” David B. Fischer, BS, a study investigator and MD candidate from Harvard Medical School, Boston, said at the 2015 American Academy of Neurology Annual Meeting.

For the study, Fischer and colleagues sought to better understand the application of neural networks in predicting the effects of transcranial direct current stimulation (tDCS) on motor modulation. They enrolled 12 healthy subjects who were right-handed and employed resting state functional connectivity magnetic resonance imaging (rs-fcMRI) to determine neural networks.

To test the hypothesis that entire network stimulation improves motor excitability vs. primary motor cortex stimulation alone, they used the motor network map to create a multifocal tDCS array.

Patients received tDCS for 10 minutes in multiple alternative arrangements. Researchers then used single pulse transcranial magnetic stimulation to test motor reactivity via motor evoked potentials of the contralateral hand before and after tDCS.

Although acknowledging that there is a lot of variability between subjects, which makes it hard to show significant differences, Fischer said they saw a trend toward a more effective stimulation of the motor system using network modulation.

“At later time points — about an hour afterwards — we saw a significant increase in motor excitability only with network modulation,” Fischer said.

Postulating on the possible reason for this delay in effect, he said it could possibly be due to tDCS not actually causing action potential, but rather changing the firing threshold of neurons.

“Once endogenous firing patterns start coursing through that area, you start to see the effects of the stimulation,” Fischer said. “So it could be that you need time for the brain to run through its own internal circuit before you see the average effects of stimulation.”

Another important finding is that stimulating the entire motor network raised the excitability of both hands.

“This speaks to the idea that what we are doing is modulating an entire motor network instead of just a particular region of the motor cortex,” he said. “And making both hands more excitable is something that there is not a whole lot of evidence for in literature right now.”

Reference

  1. Fischer DB et al. Abstract I6-3B. Presented at: American Academy of Neurology Annual Meeting 2015; April 18-25, 2015: Washington, D.C.

Video Editor: Brianne Aiken; Videographer/Producer: Nicole Blazek.

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