The following list is based on presentations by leading scientists who participated at ICNPD-2011 and ICNPD-2012. A subset of these challenges will be a focus of ICNPD-2013.
Visual prosthetics challenges
In retinal stimulation, how can the activation of neural fibers and Mueller glia be avoided?
In retinal stimulation, can the pattern of electrical stimulation accommodate for morphological/physiological changes in diseased retinal tissue?
How can the E-field blurring (i.e. mismatch between the size of stimulating electrode and phosphene visual field) be avoided in retinal stimulation?
How much does retinal and cortical remodeling in long-term visual loss/injury affects the functionality of the implant?
Eyes constantly move during saccades. To improve the long-term stability of retinal implants in the eye, would it be advantageous to use a stabilizing pad on the cable or to glue the corneal incision?
In human trials of visual prosthetics, which psychophysical measures are most relevant and should be widely adopted?
Can humans get visual percepts from phosphene primitives?
Auditory and vestibular prosthetics challenges
How long after the hearing loss, the neurons in the spiral ganglion remain viable for a successful use of cochlear implant?
Since neither temporal nor spatial pitch encoding in a cochlear implant (CI) can reproduce the harmonics and phase shifts present in natural pitch perception, perhaps the multipolar “phased array” stimulation with spatio-temporal encoding can provide a more natural-sounding pitch perception?
Perhaps the use of multipolar “phased array” stimulation may reduce the current spread?
How much of spatio-temporal encoding is smeared/blurred by current spread from adjacent electrodes?
Why the monopolar stimulation in CI is five times more effective than bipolar, even though biplolar stimulation is more spatially restricted and thus supposedly more tone-selective?
Why analog stimulation in CI is not as effective in practice as the theory would predict?
Why usually there are no more than 7-10 independent functional channels?
Does the current spread determine the limit of current steering?
Can a cochlear or vestibular implant based on intra-neural high-density micromachined electrode arrays deliver greater performance (e.g. more functional channels) than one using traditional intra-lumenal electrodes?
How can the inhibitory signaling in semicircular canals be implemented in a vestibular prosthesis? (e.g. by maintaining a high resting firing rate at a cost of reduced dynamic rage and increased power consumption?)
Motor/BMI prosthetics challenges
In developing a closed-loop bi-directional brain neural interface, how can the causality be established between the electrical microstimulation and readout that avoids the confounding influence of unrelated spontaneous neural activity?
Might the activity in the somatosensory cortex be too heterogeneous, time-varying, and otherwise complex to be successfully decoded in real time for enabling an effective brain-machine interface?
Is it possible to implement an adaptive closed-loop control of paralyzed limbs after spinal cord injury using a controller based on real-time co-adaptive model of the spinal motor pattern generator?
Challenges in neuromodulation for pain control
Can selective electrical stimulation of afferent fibers in the nerves from an amputated limb can generate an artificial sensation suppresses the phantom limb pain? (e.g. Stimulation of which afferent fiber type would be most effective – touch or proprioception of static joint position or joint movement?)
Is the pain relief in spinal cord stimulation (SCS) due mostly to antidromic rather than orthodromic stimulation?
For implementing the closed-loop SCS, how to overcome the confounding effects of varying distances of stimulating electrode and recording electrode to the spinal cord during the change in posture? (e.g. can it be accounted for by performing an initial calibration with posture-dependent recruitment curves?)
Is the additional complexity of recording from posterior (dorsal) roots is necessary considering that dorsal rhizotomy procedure works well despite its negative perception by some patients and neurologists.
Electrode-tissue interface challenges
Can the neurotrophic drugs be used to improve an interface between the electrode and neural tissue?
How to reduce biofouling of the electrode surface for long-term electrochemical sensing?
What charge transfer processes contribute to the measured voltage transient of an electrode pulsed in vivo and how to quantify these processes? (E.g. tissue resistance, concentration and activation overpotentials, cell capacitance, cable capacitance, current leakage paths, shift in equilibrium potential of redox state; side reactions)
For chronically implanted stimulating electrodes, how to determine the safe limit of polarization and what are its key contributors? (Is it primarily due to reduced counter-ion transport?)
How small can the stimulating electrode be made without compromising its ability to inject sufficient charge to neurons around the glial scar? (~50 μm diameter for SIROF electrodes?)
How can we effectively combine the expertise in device engineering, electrochemistry (charge delivery through complex tissue geometry), and materials science for making optimal neural implants?
Insulation and encapsulation challenges
Which mechanisms contribute to gradual degradation of polyimide-based electrodes and cables? (E.g. delamination?)
Gregg Suaning and Stuart Cogan:
How can the materials selection and electrode design reduce the gradual degradation of electrode insulation in vivo (E.g. silicon carbide?)
How to detect early defects/leakage in insulation and pinpoint their location (at the electrode, bonding area, cable, and/or connector), as they are not easily distinguished by any available methods – EIS, CV, or cross-talk measurements?
How can we achieve reliable high-density feedthroughs for a cortical prosthetic device with a channel count up to 1000?
How can we measure the helium leakage rate in a subminiature hermetic package (less than 1 cubic mm)?