Nerve Chips: Bridging Mind and Machine Alik Widge MEMS Laboratory Neurobotics Laboratory Carnegie Mellon University

Your Humble Speaker n Dartmouth Class of 1999 n Double major, computer science/cognitive science n Inspired by ENGS007, Fall 1995 n M.D./Ph.D. Program, University of Pittsburgh n 2 years med school n 3+ years grad school n 2 more years med school n And then residency…

Roadmap n The topic: interfaces between the nervous system and electronic devices n Why? n What could they do for us? n Do we really need that? n How? n What problems do we have to solve? n What techniques have been tried? n What will we do next?

n Control artificial limbs and organs (or anything else that can be run by a computer…) Nerve Chips: Why? n What could we do if we could tap into neural signals? Y Matsuoka, 2001 P Heiduschka and S Thanos, 1998 n Replace missing sensory data n Route them around dead or damaged tissue n But even better yet….

Nerve Chips: Why? n …expand human capabilities to the limits of human imagination

Do We Really Need That? n Neurological disorders cost $250 billion/yr in USA n Acute care, rehab, inability to work, long-term care n Stroke, injuries, birth defects, diabetes, Alzheimer’s, Parkinson’s, multiple sclerosis… n No real cure for any of these n Prosthetics exist, but hard to control n No good sensory prosthetics (except hearing) n Would you like to… n …see with better accuracy, even in the dark? n …control your environment with a thought? n …experience otherwise-impossible sensations?

Neuroanatomy in a Nutshell

What Do We Have to Do? n Get our interface into the body n Keep the body from attacking and rejecting the chip n Get close to the target nerve cells n Transmit electrical current to the targets n Don’t transmit current to non-target cells n Don’t harm the nerve with too much current n Record signals from the targets n Try to separate out the voices of single cells n Do all this to thousands of cells at the same time n Adapt to the body changing over time

How Do We Do It? (1) Nerve Cuff n Flexible cuff wrapped around a whole nerve n Mechanically stable n Not very selective n Causes muscle fatigue n Can’t use in brain n Still a popular method because it’s simple and stable P Heiduschka and S Thanos, 1998

How Do We Do It? (2) Sieve Electrode n Axons of a cut nerve regenerate through holes in silicon chip n Lets us talk to individual axons n We either have to wait for a nerve to get cut or cut it ourselves n Not in the clinic yet, but soon… L Wallman et al., 1999

How Do We Do It? (3) Microelectrode Array n Array of tiny conducting spikes n Can stick it anywhere in the nervous system n Can’t be sure every spike will hit a cell n Can damage tissue n Some clinical trials ongoing n Versions of this let you do some semi-cool things with animals PJ Rousche and RA Normann, 1998

What Can We Do Now? (1) n Cochlear Implants (hearing prosthesis) n Pick up speech sounds with a microphone n Filter digitally to reduce noise n Pass to electrode array in cochlea (inner ear)

What Can We Do Now? (2) n Functional Electrical Stimulation (FES) n Electrical stimulators similar to nerve cuff n Implant near or inside key muscles n Stimulation controlled by patient commands (remote control device) n Coordinated stimulation programs to produce hand grasp, walking, etc. n Can also trigger stimulation from sensors

What Can We Do Now? (2)

n Videos of FES Application: Correcting Foot Drop

What Can We Do Now? (3) n Visual prosthesis n Camera on glasses n Video sent to belt-pack computer for processing n 10x10 electrode array on the surface of visual cortex n Actual result: 3-5 specks of light (“phosphenes”) n Can read big text, navigate in some environments

What Can We Do Now? (4) n Multielectrode arrays to control animal behavior n RoboRat (SUNY) n Electrodes in “whisker” part of brain indicate direction n Electrodes in “pleasure” center reward for correct behavior n RoboRoach (Tokyo University) n Antennae replaced by electrode n Note large electronic backpack required for each case n Effect wears off as animal adapts to the stimuli n Any social/ethical implications?

What’s Still Missing? n All of these still use pretty big currents n Hurts the cells, rapidly fatigues the muscles if stimulating them directly n Need to be talking to a lot more cells to get true biological precision and resolution n Only one (sieve electrode) is really specific for individual cells n Can always use more mechanical stability and biocompatibility

The Next Step? n Make a chip that has living neurons built into it n Use those living cells as your connection to the patient n Nothing is better at talking to neurons than other neurons…

How Do We Get There? n Nanotechnology – design of new “impossible” materials n Electrode coatings that contain brain molecules, “trick” cells into acting like electrode is part of brain n Polymer chains that can enter the cell n Conductive polymer chains that place your electrode inside a cell without hurting it n Components that “self-assemble” through chemical forces n Other crazy stuff I haven’t thought of yet

Thanks n Advisors n Kaigham Gabriel (ECE, Robotics) n Yoky Matsuoka (MechE, Robotics) n Victor Weedn (MBIC) n Sources of Money n NIH training grant T32N n Department of the Army (NDSEG Fellowship) n Paralyzed Veterans of America n Inspiration n Dr. Joe Rosen n You