The Neuro-Cognitive Rehabilitation Research Network (NCRRN) is an NIH-funded collaboration between investigators at MossRehab and the University of Pennsylvania to provide infrastructure support and expert consultation to individuals wishing to pursue cognitive rehabilitation research. In June 2009, NCRRN co-sponsored, along with the Center for Experimental Neuro-Rehabilitation, another NIH-funded research infrastructure grant, a weekend symposium on two developing forms of electrical brain stimulation: transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS.) Over the course of the weekend, several of the world’s leading investigators of these techniques reviewed evidence for their usefulness in assessing and treating neurologic, cognitive and motor disorders, and discussed research design issues and practical constraints in advancing research on these promising techniques.

A great deal of discussion centered on the basic mechanisms of TMS and tDCS, as well as the pros and cons of each method. In TMS, stimulation is delivered through pulses from a magnetic coil situated near the skull, with the induced magnetic fields generating electrical events inside the brain. While TMS has the advantage of delivering focused stimulation, investigators cautioned that it was a technically demanding procedure, requiring an MRI scan to guide the positioning of the coil. Investigators described tDCS as a comparatively low-tech and less expensive method of stimulation. In tDCS, electrical current is applied to the scalp through a low voltage battery and saline-soaked gauze. While the stimulation is significantly less focused than TMS, the method itself is much more flexible and can be applied to patients while they are performing tasks or undergoing other treatment. Investigators also noted that tDCS was a safer procedure since it only moves neurons towards or away the threshold of stimulation instead of producing actual neuronal depolarization, which occurs during TMS.

TMS and tDCS can inhibit or enhance brain activity depending on the stimulation parameters, and several experts discussed the fact that the balance of activity between the two hemispheres can, in principle, be altered by enhancing the damaged hemisphere or reducing inhibiting unwanted suppression from the intact hemisphere. For example, if a lesion in a patient’s right hemisphere causes neglect on the left hemi-space, they explained, an investigator could attempt to stimulate activity of the right hemisphere or decrease activity of the left hemisphere. The results of such a study could determine if balance between hemispheres is as important as the activity level on either side. Similarly, one investigator, H. Branch Coslett, MD, an adjunct faculty member at MossRehab, is currently co-investigating the use of TMS in aphasia treatment. The study involves delivering inhibitory stimulation to the right hemisphere of healthy patients to see whether the remaining left hemisphere language capacities express themselves more fully.

The use of TMS in aphasia treatment reflected a broader theme of the symposium, which was the increasingly popular use of brain stimulation to treat cognitive issues in addition to motor control problems that have been studied for longer periods. Of particular interest was the effect of frontal lobe stimulation on executive function, and its potential to treat individuals with self-control problems, such as cigarette smokers, substance abusers, and those with obesity. Investigators presented preliminary research showing that tDCS applied to the prefrontal cortex can suppress immediate urges and possibly stimulate healthier long-term health-related behaviors. The neuro-ethical implications of such treatment were also discussed, in view of the fact that many individuals without brain damage have less self-control than they might wish.

Summaries of the discussions as well as PowerPoint presentations have been posted on the NCRRN web site: http://www.ncrrn.org/papers/symposium_summaries_0609. The results of exercises in which attendees designed hypothetical research protocols for a range of different treatments are also posted online. Select portions of the symposium will be reprieved at the International Brain Injury Association Meeting in 2010.