Neural Engineers Come to Salt Lake City for 2012 Neural Interfaces Conference
by James Cavuoto, editor
About 500 neural engineers, researchers, clinicians, and vendors attended the 2012 Neural Interfaces Conference in Salt Lake City earlier this month. The biannual meeting is an offshoot of the NIH Neural Interfaces Workshop and it still receives funding from NIH as well as DARPA and the National Science Foundation.
In the first session, Zelma Kiss from the University of Calgary gave an overview of neuromodulation therapies for treating chronic pain. She reviewed previous efforts using DBS of the periventricular gray and somatosensory thalamus, which were abandoned, and also cortcial stimulation, peripheral nerve stimulation, and spinal cord stimulation. A recurrent theme she identified was indication/device creep, whereby vendors market an existing device for new indications or clinicians use an old device for a new application.
Karen Davis from the University of Toronto highlighted some of her work in functional imaging of chronic pain. Working with patients with irritable bowel syndrome, she noted that connectivity between the insula and cingulate might serve as an indicator of chronic pain.
Stewart Tepper from the Cleveland Clinic spoke about peripheral nerve stimulation for treatment of headache pain. He reviewed the levels of evidence for gauging the quality of pain studies, which range from class A, which includes two randomized controlled trials, to classes C and U, with much less perceived validity. Tepper lamented the relatively low levels of evidence for neuromodulation trials but also noted that opioid administration can interfere with pain studies and recommended that clinicians wean patients from overused medications. With respect to migraine, he said it doesn’t take much opioid use to transform a mild migraine patient into a constant sufferer.
Tepper is a collaborator with Autonomic Technologies, which recently received CE Mark approval in Europe for its RF activated stimulator implanted in the sphenopalatine ganglion. He compared preliminary results from an open-label trial of the device for treating cluster headache to data from previous efforts with occipital nerve stimulation. He noted that Medtronic’s ONSTIM trial showed a 39 percent responder rate, St. Jude Medical had a 41 percent responder rate after 12 weeks, and Boston Scientific’s PRISM study did not meet its primary endpoint. With the ATI device, by contrast, two-thirds of participants experienced acute pain relief within 15 minutes and there was a drop in the frequency of attacks. Some participants reported tingling, numbness, or dry eye in response to the SPG stimulation, though Tepper pointed out that since the device is screwed into the skull, there is no chance for lead migration and no tunneling or IPG to worry about.
On the second day of the conference, presenters discussed challenges confronting design and clinical use of DBS systems. Cameron McIntyre from the Cleveland Clinic reviewed clinical factors in the treatment of Parkinson’s disease, noting that dopamine replacement causes sufferers additional problems such as dyskinesia and that many neurologists seek to obtain a balance between drug use and stimulation in their patients. He stressed that DBS is a network modulation tool useful for interacting with oscillatory loops in the brain.
Erwin Montgomery of the University of Alabama lamented that DBS has only reached a small fraction of its potential patient population, particularly since it is a better treatment than any medication for Parkinson’s disease. Instead of the approximately 1 percent penetration DBS now has, he feels it should be more like 10 to 15 percent. He also pointed out that there is a disturbing tendency for some clinicians to give up on DBS therapy and go back to medications rather than play with programming parameters.
According to Montgomery, part of the problem is that theories of DBS action are based on models of pathophysiology which are wrong. Also, there can be wide variance in the delivery of current to the target and if the variance is large than typical programming parameters are useless. The patient’s unique regional anatomy should determine the appropriate placement of electrodes and stimulation parameters. The goal, he said, should be to sculpt the electrical field to conform to the target without spilling over to other targets.
Tammy Hershey from Washington University addressed the issue of cognitive and mood effects within Parkinson’s disease and reported that DBS of the subthalamic nucleus can worsen these problems. This assessment is made more difficult by the uncertainty caused by the progression of the disease and flux in medication levels. She found wide individual variability and reported that the choice of contact within STN could have an impact on cognitive and mood side effects of stimulation. More ventral locations corresponded to cognitive impairment while more medial contacts correlated with mood disturbances. She recommends that clinicians map contacts well and then test those contacts before settling on a therapeutic regimen.
Jay Albers from the Cleveland Clinic looked at postural side effects of DBS for Parkinson’s disease and noted that STN has a unique anatomy that may lead to current spread. He said that five years after implantation, up to 35 percent of patients have worsening postural stability.
Warren Grill from Duke University described his model of the informational lesion in postulating a mechanism of DBS action. He reported that non-regular stimulation decreases effectiveness and that there is correlation between beta band power and DBS effectiveness. Grill suggests that temporal stimulation pattern may be a valuable new parameter for DBS therapy. McIntyre is also examining the effect of different waveforms, such as triangular center vs. rectangular shape, as a result of computing the biophysical efficiency. He said that center triangle pulses have a 15 percent reduction in energy consumption compared to rectangular with dynamic compliance current controlled IPGs.
On the third day of the conference, Robert Kirsch from Case Western Reserve University described his efforts to integrate BMIs with functional stimulation. He argued for effective local feedback control when commanding FES systems.
[excerpted from Publisher's Letter]
The FDA sent two representatives to the meeting to advise attendees on strategies for getting device approvals. Kristin Bowsher from CDRH’s Office of Device Evaluation described a new “Innovation Pathway 2.0” that potentially streamlines early feasibility trials. Though the proof of principle program is not accessible to everyone at this point, it does at least open the door to the possibility of speeding up the approval process for some Class III devices.
Cristen Welle from CDRH’s Office of Science & Engineering Laboratories described some of her team’s efforts to refine regulatory science in an era of new materials, new forms of stimulation, and new types of interactions between implanted stimulation devices and living tissue. It was encouraging to see a regulator with an understanding of issues such as charge density per phase, excitotoxicity, and changes to ion channels. Indeed, her lab conducts its own experiments on long-term safety and reliability of neural interface devices. And while she stressed that the FDA approves devices and not materials, she advised that there is a master file by which the agency collects information that can be accessed when a new submission comes in.