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Neuroprosthetics . Week 6 Design Issues. Neuroprosthetic Devices. Three basic types 1. Use neural signals as an input, possibly to control a mechanical device 2. Based on some action, transmit a signal to a nerve for a desired response

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Week 6

Design Issues

neuroprosthetic devices
Neuroprosthetic Devices
  • Three basic types
  • 1. Use neural signals as an input, possibly to control a mechanical device
  • 2. Based on some action, transmit a signal to a nerve for a desired response
  • 3. Those that have neural inputs and outputs – bypassing spinal cord damage
devices with neural input
Devices with neural input
  • Operation based directly or indirectly on neural activity
  • Measurements interpreted to create control signals for an external device
  • Feedback is usually either:
  • Confined to the neuroprosthetic device itself, or
  • Is via the body’s natural senses
devices with neural output
Devices with neural output
  • Stimulation arises from an external trigger
  • Signal is processed and tailored for transmission to a nerve
  • Neuromuscular stimulation involves the transmission of a signal , via electrodes, to a muscle
devices with neural input and output
Devices with neural input and output
  • Device modifies a nerve signal to achieve a desired goal
  • Challenges of accurate input interpretation and appropriate interpretable output are significant
  • Such devices tend not to have significant material or power requirements – no aerial for example
signal measurement
Signal Measurement
  • Measure signal from neural inputs over time without medical intervention
  • Must not be subject to an inhibitory body response or side effects
  • Any surface electrodes must be placed to avoid abrasion or local pain
  • Development needed for body state measurement
  • Reliability is key
signal interpretation
Signal Interpretation
  • Network (Neural) is nonlinear and complex
  • Even with ANNs, internal signals are not meaningful
  • Correlation between measured neural signal and intended action is a challenge
  • Often signals have no apparent or simple meaning
  • Artificial devices are usually first order approximations to complex nonlinear relationships
intent interpretation
Intent Interpretation
  • Inputs indicate state of the body
  • Body tissues will respond to any signals input
  • Feedback mechanism is in place
  • If a specific signal is input, what will the body likely do in response?
  • Whole body focus necessary
action performance
Action Performance
  • Device must be able to adequately perform an action
  • Power and material type are critical
  • Prosthetic limbs – sufficient power required to lift and manipulate objects
  • Battery lifetime is important – minor surgery for replacement
  • Inductive power supply is an alternative to a battery – less needs to be implanted
  • Induced emf in implanted coil, related to external exciting coil current is:
  • E = -nAdB/dt
  • A is area of receiver coil
  • dB/dt = KIw
  • I = amplitude of exciting current
  • w = frequency of exciting current
  • K is a constant
signal generation transmission
Signal Generation & Transmission
  • Inserting a neural input into the complex network – understanding of other possible results than just desired action
  • E.g. muscle fatigue and cramps can occur
  • Long term approach for reliable and robust signal transmission onto/into nerves
  • Devices must be supported – so not adversely affected by movement
  • Devices must not cause irritation or other problems
prosthetic arms
Prosthetic Arms
  • Loss of a limb is a traumatic experience whether through disease or accident
  • Limbs are the primary way in which humans interact with the world
  • Amputees have an expectation of a prosthetic arm’s performance
  • Many amputees expect their prosthetic arm will be much more powerful than the original – due partly to science fiction!!
  • So huge challenge both technical and social
state of the art
  • An ideal prosthetic arm would replace all natural functions:
  • Strong, gentle, fast, high precision, stiffness range, sense heat and pressure
  • Must look and move as a natural limb
  • Arm must respond correctly to neural signals
  • Most common, commercially available – Boston Arm, Utah Arm
commercial arms
Commercial Arms
  • Performance of commercial arms is well short of original arms
  • Boston elbow can lift only 9lbs
  • Speed varies with orientation to gravity – Utah arm flexes in 1.1 secs
  • Utah has powered free swing in walking
  • Switching from walking to normal mode
  • Removable, rechargeable batteries – do not provide enough energy for one day’s use
  • Control of a hook or hand provides even more problems
prosthetic arm signals
Prosthetic Arm - Signals
  • Commercial arms use myoelectric activity measured using surface electrodes
  • Electrodes typically are mounted in the limb socket – sit on stump surface
  • Superimposed muscle signals are recorded
  • Other inputs include cables and switches to convert other body movement actions
  • Surface electrodes now starting to be used
  • But this is complex + suffers from skin irritation and extraneous signal components
cochlea implants
Cochlea Implants
  • Signals from microphone transmitted to implanted electrodes in the auditory nerve
  • DSP used to extract features
  • No claim that hearing is restored
  • User can usually recognise speech – assisted with lip reading etc
  • Prefer no visible signs of implant
  • Power, size, SP problems
  • Loss of bladder control has social implications as well.
  • Regaining bladder control allows an individual to be part of society again
  • Vocare (commercial) system provides an external unit which controls bladder emptying
  • Signals are transmitted to an implanted receiver – activates appropriate nerves
  • Future – smaller, less obtrusive and allow user overall control without external trigger.
next week
Next Week
  • Cochlea Implants