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Neuroprosthetics

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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. – PowerPoint PPT presentation

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Title: Neuroprosthetics


1
Neuroprosthetics
  • Week 6
  • Design Issues

2
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

3
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 bodys natural senses

4
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

5
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

6
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

7
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

8
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

9
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

10
Power
  • 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

11
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

12
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
    arms 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

13
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

14
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 days use
  • Control of a hook or hand provides even more
    problems

15
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

16
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17
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

18
Bladder
  • 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.

19
Next Week
  • Cochlea Implants
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