Neural Control for Upper Limb Flashcards
What are the three methods for mind-controlled of motorized prosthetics?
- Myoelectric system
- Peripheral nerve electrodes
- Brain-computer interfacing strategies
What are pros and cons of peripheral nerve electrodes?
Pros: recruitment of signals from transected nerves enables more intuitive control
Cons: Spatial resolution is dependent on invasiveness of the electrode (short-lived due to foreign-body response)
What are pros and cons of BCI strategies?
Pros: suitable for patients without available or functional peripheral nerves
Cons: Cortical electrodes are surgically invasive, infection risk
What are the different degrees of invasiveness for central control? (3)
EEG - on the surface, least resolution of signal
ECoG - on the surface of cortex, more invasive, more resolution
Intracortical - most invasive, most resolution
Different types of ECoG (2)
Subdural - more invasive, but much better signal quality; most common
Epidural - less invasive, signal quality for BCI may not be as good
But, if using larger scale electrodes, no real difference between them
What do you need to consider when designing a neural interface? (4)
- Signal quality
- Ability to process
- Real-time application
- What effector technique is being used
Population coding for movement directions (Georgopoulos and co)
Concept that motor neurons change firing rates in response to the direction of movement required.
Found that motor cortical neurons would discharge at increased rates when movement was required in the “preferred direction”
What is the “tuning curve”
Multiple motor cortical neurons have their own “tuning curve” which is the angle that they will fire most at (or be inhibited at)
Utah Electrode Array
100 1.5mm microneedles from a 4x4x0.2mm. Tips coated with iridium oxide making each one a microelectrode
Explain the cortical control of robotic hand by monkeys (Andrew Schwartz)
Implemented two monkeys with 116 electrodes in cortical arrays in the motor cortex that directs arm movement.
Recordings were processed through a computer and signals directed to a robotic arm, monkeys were trained to feed themselves with the robotic arm.
A program updated the electrode that was firing to match the direction the monkey wanted the arm to move.
How did the monkeys adapt and what new behaviors did they do? (4)
- Licked remaining food off fingers
- Used the hand to push food into their mouths
- Moved the arm in arcs to avoid knocking the food off the platform
- Found out with sticky food hand could be opened earlier
What other areas of the central nervous system has shown activity of neurons being related to direction of movement? (3)
- Supplementary motor cortex
- Basal Ganglia
- Cerebellum
What were the effects of the man who removed his left somatosensory cortex? (Richardson et al) (3)
Unable to:
1. Feel any light touch, pain, temp, or vibration in right hand/arm
2. Sense proprioception, tactile movement, graphesthesia, and stereognosis gone in the right hand/arm
3. Had positive Romberg sign (loss of proprioceptive input)
Describe how stimulation can be used to recovery somatosensory function
Via intracortical microstimulation of the somatosensory area. Implant two 32-electrode arrays on patient with tetraplegia.
Required 3 electrodes being stimulated to get sensation, then only 1 channel after getting used to it. Sensation was like pressure.
All the studies in this PowerPoint
Just go look at the notes, it’s not cue-cardable (Slides 37-46)
What are some field potentials of EEG
Muller-Putz and colleagues have shown EEG of brain patterns can control a robot arm in 2 DoF.
Using EEGs hope to avoid the issues that arise from invasive surgeries and the electrode movement/tissue damage after the fact.
What are the EEG brainwave frequency ranges?
Alpha: 7.5 to 13.5 Hz (best known)
Beta: 13 to 30 Hz
Delta: 1 to 4 Hz
Theta: 4 to 8 Hz
Gamma: 30 to 70 Hz (linked to cognitive processing)
What is a possible future direction for controlling limb prosthetics?
Recording signals (ENG) directly from motor nerves to control the prosthetic. Can use devices such as Nerve cuffs, LIFEs, electrode arrays, or Sieve Electrodes
Nerve Fascicles
Individual axons bundled into groups called fascicles, surrounded by connective tissue perineurium.
Either sensory or motor in nature.
Extraneural Electrodes
Record and stimulate from outside the nerve; low selectivity for recording and stimulating individual axons.
Ex. Nerve cuff electrode - surrounds nerve.
Flat-Interface Nerve Electrode - gently flattens nerve between array of extraneural electrodes
Intraneural electrodes
Penetrate the nerve and record and stimulate individual or small clusters of nerve fibres. Greater selectivity for recording and stimulating axons, requires lower stimulus intensities
What is LIFE?
Longitudinal Intrafascicular Electrodes
Intraneural electrode. Thin electrode inserted into individual nerve fascicles, biocompatible and removal does not require surgery
What is USEA?
Utah Slanted Electrode Array.
Intraneural electrode array inserted into the side of a nerve. Increased sensitivity due to large number of electrodes, but rigid structure can cause some damage to nerves.
What is the goal of regenerative electrodes?
Development of regenerative electrodes is to obtain an extensive, stable and bidirectional electrical contact with peripheral nerves.
Placing sieve electrodes in regeneration pathway of severed nerve fiber causes it to regenerate through its
different holes and enabling selective stimulation and recording of the neural bioelectrical potentials
