Lecture 12 - Neuroprosthetics

Question 1

What is a neuroprosthesis?

Answer 1

An interface that connects to the neural system (brain and/or nerve signals in periphery). Signals which cannot propagate through the spine anymore (due to e.g. spinal cord injury) can be bypassed via the neuroprosthetic device to the periphery.
A device that bypasses or replaces a missing body function by interfacing the nervous system via sensing and/or stimulating nerve connections.

Question 2

What is the difference between an input and an output neural interface?

Answer 2

An output neural interface acts as a BCI; it detects motion intention signals (e.g. via EEG, EMG, fNIRS), processes them in a CPU and then outputs them via some output device.
An input neural interface receives input from a button, video (e.g. gait analysis), sound or image and translates it into stimulation of sensory or motor function of the body.

Question 3

What is an input neural interfaces?

Answer 3

• Recording of information from the environment (or human) and conversion into artificial stimulation signals
• Stimulation of afferent signals, i.e. sensory perceptions (e.g. cochlear or retina implants) or efferent signals, i.e. movement (e.g. foot drop stimulator)

Question 4

What is an output neural interface?

Answer 4

• Recording of info. from brain or nerves/muscles, conversion into intention signals
• Signals help drive external devices (e.g. computer, kitchen device) or support the body (e.g. exoprosthesis, wheelchair)
• Brain Computer Interfaces (BCI) are usually part of output neural interfaces, if the processed signal provides a prosthetic function

Question 5

What elements makes up a Brain Computer Interface?

Answer 5

Signal Acquisition -> Signal Processing ( Feature Extraction + Pattern Recognition) -> Control System -> Feedback

Question 6

Give examples of non-invasive brain recordings for BCI.

Answer 6

• EEG, MEG

- fNIRS

Question 7

Give examples of invasive brain recodings for BCI.

Answer 7

• Intracortical electrodes

- Intracortical implants

Question 8

Compare Surface FES Electrodes vs. Invasiv/Implanted FES Electrodes.

Answer 8

Surface Electrodes
- non-invasive, onto skin
- medium conducts current to underlying skin (e.g. water, conductive gel)
Invasive Electrodes
- percutaneously inserted through skin
- implanted under skin (permanent) e.g. cuff electrodes or intramuscular electrodes

Question 9

What are the advantages of Surface Electrodes?

Answer 9

• non-invasive
• multile muscles can be stimulated with a single electrode
• easy to apply
• generally inexpensive

Question 10

What are the disadvantages of Surface Electrodes?

Answer 10

• poor selectivity
• no option of stimulating deeper located muscles
• stimulation response depends on electrode positions; needs time to reposition electrodes
• high voltage required

Question 11

What are the advantages of Implanted Electrodes?

Answer 11

• good selectivity
• constant stimulus perception response
• surface and deep muscles stimulated; leads to higher forces
• lower voltage required

Question 12

What are the disadvantages of Implanted Electrodes?

Answer 12

• invasive

- safety (risk of infection, broken electrode parts)

Question 13

What pulse frequency is needed for FES stimulation patterns?

Answer 13

• must be high to get smooth contractions
• however, higher frequency results in stronger fatigue
• idea freq: 15-25Hz

Question 14

What pulse current and pulse duration are needed for FES stimulation patterns?

Answer 14

• increase pulse amplitude or pulse duration (width) increases charge delivered to motor units
• more charge leads to stronger contractions
• too high charge stimulated pain receptors
• pulse duration: 100-500 microsec.
• current amplitudes below 100mA