State-of-the-Art Neurotech Presented at 2005 Neural Interfaces Workshop

by James Cavuoto, editor

The 2005 Neural Interfaces Workshop, held September 7-9 in Bethesda, MD, offered attendees an excellent opportunity to observe the state of the art in neurostimulation technology. As it did in 2004, the event combined the annual Neural Prosthesis Workshop—now in its 36th year—and the DBS Consortium.

This year’s workshop included a few new features, including opening presentations from neurotechnology users on their experiences with their systems, and two “platform presentation” sessions in which poster presenters were given a brief opportunity to summarize their posters. The first day of the event was largely devoted to advances in deep brain stimulation (DBS) systems. Jerrold Vitek from the Cleveland Clinic led off with his view of clinical challenges facing the DBS community [see article, p1]. Among these are finding new targets for stimulation, identifying nonmotor symptoms of movement disorders, and more standard methodology in long-term studies of DBS.

Arguing against a one size fits all approach, he called for the design of new leads that would be specific for each site in the brain and for each specific disorder being treated. Vitek also broached the subject of perhaps administering DBS therapy earlier in the progression of the disease, suggesting that leaving abnormal neural activity untreated for too long might have an adverse effect on later treatment outcome.

Following Vitek, several DBS practitioners and researchers presented findings related to mechanisms of action, stimulation parameters, motor and cognitive effects, and potential new types of stimulating electrodes. Several presenters spoke of synchronized oscillation of basal ganglia cells within low frequency ranges in Parkinsonian patients, suggesting that higher-frequency STN stimulation may desynchronize this pathological oscillation. Robert Turner from UC San Francisco reported “downstream” effects of DBS in motor cortex, mentioning that STN stimulation can activate cortical neurons antidromically, which may offer implications on therapeutic approaches.

A team from Arizona State University and Sandia National Laboratories described their proposed thermal microactuated microprobe, which would allow precise positioning of DBS leads. The device is capable of translation up to 9 mm in length in steps of 8.8 microns. Jun Li from NASA Ames Research Center described his team’s work with carbon nanofibers as a potential new form of neural interface.

The second day of the workshop dealt with advances in a variety of neural prostheses. Michael Keith from Case Western Reserve University updated the audience on progress with the upper-extremity prosthesis for treatment of tetraplegia. The Cleveland team has moved to a 12-channel myoelectric controlled device, which represents a next generation of the Freehand hand grasp stimulator previously marketed by NeuroControl Corp. The system uses nerve cuff electrodes to help select individual fascicles within the radial nerve.

Kensall Wise from University of Michigan described his team’s work with three-dimensional thin-film intracortical recording arrays. The 64-electrode arrays are decoupled from the skull, allowing them to “float” with brain tissue. Philip Kennedy from Neural Signals Inc. described his team’s novel and nascent effort to construct a speech prosthesis by performing phoneme recognition in Broca’s area of the brain. Charles Della Santina from Johns Hopkins University described progress on a vestibular prosthesis that encodes head movement in three dimensions.

Mark Humayan from University of Southern California and Second Sight presented results from six subjects who have been implanted with the firm’s 4 x 4 electrode grid retinal implant for periods ranging from 13 to 41 months. The company is planning a second generation 60-electrode device as an interim step preceding the high-resolution 1000-electrode system, which they hope will restore the ability for face recognition and mobility to blind users.

The final day of the workshop looked at future directions in neural prosthesis development. Theodore Berger from University of Southern California presented his team’s work on an implantable hippocampal prosthesis. Duco Jensen from Vanderbilt University described his research into optical stimulation of neural tissue and discussed its potential as a replacement for implanted electrical stimulation devices. Jansen demonstrated induction of action potentials in discrete neural populations within sciatic nerve. He identified an optimal wavelength of 2.1 microns using a free electron laser and was able to achieve spatial selectivity and conduction velocity similar to electrical activation.

Miguel Nicolelis from Duke University, who has worked extensively in the area of brain machine interfaces, described work in several new applications. His laboratory is developing a sensory feedback system using a 16-element vibro-tactic stimulator whose output is proportional to joint angle. His goal is to create a receptive field within motor cortex in order to induce “fake” proprioception in subjects deprived of sensory input. Nicolelis is also working on a mouse model of Parkinson’s disease and has created a dopamine-depleted mouse in order to induce akinesia. He intends to examine whether vagus nerve stimulation can produce asynchrony in phase-locked cells as a possible treatment for rigidity.

The workshop concluded with a panel discussion on the future of neural prostheses in which Geoff Thrope from NDI Medical presented a retrospective look at the commercial failure of NeuroControl’s Freehand device. Thrope, who was an executive at NeuroControl Corp. during the product’s launch, plans to market a second-generation Freehand, avoiding some of the problems that faced the original system.

Other commercial firms present at the workshop included MedEl, DelSys, Guidant, Cyberkinetics, Medtronic, Advanced Cochlear Systems, Plexon, Foster-Miller, and BioNeuronics.