Neuroprosthetics

1. Neuroprosthetics Week 1 Introduction

2. Contact • Kevin Warwick • Room 171 • Ext. 8210 • k.warwick@reading.ac.uk • www.kevinwarwick.com

3. What is a Neuroprosthetic?- Traditional Definition • It is a device which replaces nerve function lost as a result of disease or injury. • The neuroprosthetic can act as a bridge between functioning elements of the nervous system and nerves over which control has been lost. • Can be used in the spinal cord to allow standing in paraplegics. • Can be used to restore hand and upper limb movement in Tetraplegics.

4. What is a Neuroprosthetic? • A neuroprosthetic may act as a bridge between the nervous system and a physical prosthesis. • This can be the case in upper limb replacement for amputees.

5. What is a Neuroprosthetic? • Intelligent Hand Prosthesis

6. What is a Neuroprosthetic? • A neuroprosthetic can augment or replace damaged or destroyed sensory input pathways. • It records and processes inputs from outside the body and transmits information to the sensory nerves for interpretation by the brain. • Examples: Cochlear implant to restore hearing, retinal cortex prostheses for restoring vision, extra sensory input.

7. Nerve Interaction • Common component is the need to interact directly with nerves. • System must collect signals from nerves and/or generate signals on nerves. • Interaction may be with individual nerve cells and fibres or with nerve trunks containing hundreds to millions of axons. • Must understand and speak the language of the nervous system. • The language changes as the signalling requirements change – e.g. auditory and optic nerves very different.

8. Potential Impact • Subject is in its infancy. • Could help extend lifespan, alter workforce, assist healthcare. • Could lessen physical and psychological impact of injury or disease. • Potential to extend and enhance human capabilities – Cyborgs. • Ethical questions – Therapy and Enhancement.

9. Uses and potential uses ?

10. Uses + • Cochlear, retinal, optic nerve • Nerve stimulation for foot drop. • Sacral nerve stimulation to prevent/control shitting. • Artificial genitourinary sphincter to control sexual activity!! • Nerve stimulator for long term artificial respiration. • Pain control via spinal cord. • Chronic Deep brain stimulation.

11. From I,Cyborg page 306 • “The human brain and spinal cord are linking structures that can be changed through stimulation. All the disabilities that spinal cord injured patients have arise from disordered nerve function. Potential benefits of the use of implant technology include:” • Re-education of the brain • Prevention of spinal deformity • Treatment of pain • Assisting bladder emptying • Improving bowel function

12. From I,Cyborg page 306 • Treatment of spasticity • Improvement of respiratory function • Reduction of cardiovascular maleffects • Prevention of pressure sores • Improvement/restoration of sexual function • Improved mobility • Improved activities of daily living

13. Evolution of neuroprosthetics • Early experimentation • Key tools • First successes • Rapid expansion

14. Experimentation • 18th Century – Luigi Galvani contracted frog’s muscles, Allesandro Volta connected a battery to his ear for an aural sensation. • 1934 – first electronic hearing aid • 1957 – first cochlear implant (first successful commercial product not until 1980) • 1961 – first motor prosthesis • 2000 – tremor control for Parkinson’s

15. Key tools • 1947/63 – transistor and integrated circuit developed – particularly useful as an amplifier • 1952 – Hodgkin and Huxley’s model of neuron behaviour (based on squid neurons) – action potentials • 1971 – microprocessor allowed rapid processing of electrical signals • 1977 – VLSI provided transistors the size of a neuron • 1981 – first (IBM) pc allowed experimentation, modelling and control • 1990’s – scanning tunnel microscope enabled visual exploration

16. First successes • 1957 – first cochlear implant by Djourno and Eyries – consisted of electrodes placed in the auditory nerve, which were stimulated at different pulse rates • 1970s – clinical trials begun in USA • 1961 – first motor prosthesis for foot drop in hemiplegics • 1980s – Functional Electrical Stimulation (FES) of motor nerves and muscles shown to be valid • 1990s – neural prostheses developed (trialled) for standing and for upper limbs • 1990s – urinary incontinence systems trialled

17. Rapid expansion • Last 10 years has seen an incredible growth in the field • 1998 – bladder controller commercially available • 2000 – middle ear implant and auditory brainstem implant • 2001 – self-contained heart replacement and sub-retinal tests • 2002 – first implant tests on a healthy volunteer – enhancements!

18. How do neurons communicate ? • Before talking to nerves and neurons it is important to know how they talk to each other. • Monitor signals transmitted to a stimulus and correlate signal features with stimulus information. • Most nerves communicate via Action Potentials – these are complex signals generated by ion movements across neuronal membranes. • Recording devices must intercept voltages and ionic currents. • Implementing such a device is complicated because of the micrometer scale of neurons and the small changes (millivolts at most) in membrane potentials – all in the presence of noise!

19. How do we communicate with neurons ? • We must manipulate voltages and inject currents to make ourselves heard by the correct cell group without damaging either cells or surroundings. • This is ongoing research – lots we don’t know yet. • Impaling a cell with an electrode is direct but the cell may well die as a result. • Key issues are: 1. amplitude of stimulating signal, 2. duration and polarity of the signal, 3. spatial selectivity. • Balanced biphasic charge best represents natural ionic currents, but how can this be delivered. • Questions: surface area, conductivity, geometry, materials, architecture, power requirements.

20. Implant Durability • System must operate successfully for extended periods in a hostile environment. • Device must be palatable (or invisible) to the natural defence mechanisms of the body. • A number of materials have been identified as being “safe”. They can perform the basic functions required from carrying electrical charge to providing insulation. • Long term effectiveness also depends on wound healing. Encapsulation increases the distance between implant and cells. Implant movement can be detrimental.

21. Course Structure • Week 2 – Implant Technologies • Week 3 – Neuron modelling • Week 4 – Stimulating/recording nerves • Week 5 – Design issues • Week 6 – Cochlear implants • Week 7 – Visual Neuroprostheses • Week 8 – Motor Prostheses • Week 9 – Emerging Technologies • TBA – Mark on our experimentation