Neural Prosthetics

Question 1

What is a neural prosthesis, and what does it require?

Answer 1

A device that can substitute or augment a sensory, motor or cognitive function; designed to be small and minimally invasive; Requires interdisciplinary research in neuroscience, psychology and biomedical engineering; and detailed knowledge of nervous system anatomy and physiology

Question 2

From the pinna and auditory canal in the outer ear, air pressure travels through which regions of the middle ear before reaching the cochlear?

Answer 2

Tympanic membrane, ossicles and oval window

Question 3

Which hair cells in the organ of corti contain more neurons connected to spiral ganglion cells, and what is their function?

Answer 3

Inner hair cells; They generate most of the auditory information (whereas outer hair cells change the rigidity of the basilar membrane)

Question 4

Describe how frequencies are place coded along the basilar membrane

Answer 4

High frequencies are coded in the base and low in the apex

Question 5

When hair cells respond to their characteristic/preferred frequency, what happens when there’s a higher sound intensity?

Answer 5

More action potentials are fired

Question 6

There are many synapses occurring before auditory information travels to the auditory cortex. Describe the pathway strarting from the spiral ganglion cells

Answer 6

The bundles of cells become the auditory nerve, then action potentials fire to cochlear nuclei > superior olivary nucleus > inferior colliculus > medial geniculate nucleus > auditory cortex (both ears send info to both hemispheres)

Question 7

What can a cochlear implant replace?

Answer 7

The activity in the basilar membrane no longer working (dead inner hair cells)

Question 8

Describe how cochlear implants work

Answer 8

A microphone decodes sound in the world, then transmits them through the transmitting coil to electrodes in the cochlear; tells it which pins to encode; the fewer the electrode channels, the coarser the sound

Question 9

What have Moore and Shannon shown about the performance of various implant users on word recognition tasks?

Answer 9

People with cochlear implants perform the best (up to 100% correct words), with auditory brainstem implant (ABI) users performing the worst (0-20%)

Question 10

How does the effect of age of cochlear implantation impact on hearing fidelity (P1 auditory evoked cortical potential)?

Answer 10

The range of the auditory system has more capacity when younger (the younger the better); after 6.5 yrs they still get some benefit but don’t hear in the normal range

Question 11

What are the 3 perceptual dimensions that relate to the physical dimensions of electromagnetic radiation in vision?

Answer 11

Hue - wavelength; Brightness - intensity; Saturation - purity

Question 12

Light must travel through ganglion and bipolar cells before reaching photoreceptors at the back of the eye (and then back again) What do photoreceptors contain, and at what point do action potentials start to fire?

Answer 12

They contain pigments that react to light; action potentials start at the ganglion cells; all activity before this is only chemical transmission

Question 13

Cones are focused in the fovea and rods in the periphery. Describe the 3 cone types

Answer 13

S-cone (short waves) code for blue; M-cones (medium) code for green; L-cones (large) code for red; each overlap

Question 14

Does visual information reaching the temporal side travel ipsilaterally or contralaterally through the optic chiasm and LGN to reach V1?

Answer 14

Ipsilaterally (nasal side travels contralaterally)

Question 15

In the retina, many photoreceptors map to a single ganglion cell. Once photoreceptors increase their excitability to bipolar cells, what do bipolar cells do?

Answer 15

Middle ones increase the chance of firing action potentials in ganglion cells, and outer ones inhibit/decrease firing (inhibitory graded potentials); ganglion cells contain on/off cells (on cells fire when light is presented in centre and inhibit in periphery; opposite for off cells)

Question 16

What do ocular dominance columns in V1 help us to discriminate?

Answer 16

Edges/orientations of objects in the world (each neuron responds best at a particular orientation)

Question 17

What does macular degeneration refer to?

Answer 17

It’s when photoreceptors in the macular (central portion of the fovea) start to degenerate; occurs as a function of age

Question 18

What does retinitis pigmentosa refer to?

Answer 18

Tunnel vision; vision from periphery is lost and the patch of visual field becomes narrower; it’s an inherited condition

Question 19

In a spectacle mounted “bionic eye”, a camera in the glasses captures an image and sends information to a microprocessor. The microprocessor then converts data to an electronic signal and transmits it to the receiver. Then what happens?

Answer 19

The receiver sends signals through a tiny cable to an electrode panel (intraocular implant) on the retina; the retinal implant emits pulses which travel through the optic nerve to the brain, which then perceives patterns of light and dark, corresponding to the electrodes stimulated on the retinal implant

Question 20

When there’s a patch of retina that doesn’t have receptors, what kind of implant will take over the job?

Answer 20

Sub-retinal implant

Question 21

In Zrenner et al.’s study, they surgically implanted a light-sensitive, externally powered microchip subretinally near the macular region of Ps blind hereditary retinal dystrophy. How does it work?

Answer 21

It contains 1500 active microphotodiodes, each with its own amplifier and local stimulation electrode; visual scenes are projected naturally through the eye’s lens onto the chip under the retina; the chip generates pixel patterns which release light-intensity-dependent electric stimulation pulses; these chips were demonstrated to create detailed meaningful visual perception for Ps

Question 22

Compare the two motor corticospinal pathways

Answer 22

Dorsolateral - control distal muscles (e.g. hand; fingers) on opposite side of the body (reaching and grasping); Ventromedial - control proximal muscles (e.g. shoulders) on both sides of the body (posture and walking)

Question 23

Describe the hierarchical control in the sensorimotor system

Answer 23

Association cortex (prefrontal and parietal - planning/executive control) > secondary motor cortex (premotor; supplementary motor) > primary motor > brainstem motor nuclei > spinal motor circuits; complex feedback loops between all (e.g. if an error’s made in execution, info sent back to prefrontal/parietal to reassess, etc)

Question 24

Monkeys have been trained to move a joystick to control directions of movement. When patterns of action potentials in the primary motor cortex are more dense, what does this mean?

Answer 24

This is the preferred direction encoded by a particular neuron

Question 25

In a tetraplegic patient who had suffered a spinal cord injury, Hochberg et al. implanted 100 tiny electrodes into the part of his motor cortex which would normally control arm and leg movements. When he was asked to imagine performing certain movements, what occurred?

Answer 25

The same neurons were activated as if really performing the task (mirror neurons); there was also an increase in firing rate of action potentials when asked to imagine pulling his hands apart/together (clapping), and when closing his hands

Question 26

Describe another case in which Hochberg et al. helped a tetraplegic patient after a brainstem stroke

Answer 26

They connected an algorithm that decodes patterns of firing to a prosthetic limb (robotic arm), and she was able to grasp a cup and take a drink using her thoughts

Question 27

Describe how the brain-controlled typewriter works

Answer 27

By using SSVEPs (via EEG) to create a brain computer interface (BCI), which decodes the flicker of frequencies from the visual cortex; the participant focuses on each flickering letter and the word gets typed

Question 28

What are some future challenges for neural prosthetics?

Answer 28

Fidelity; battery power; tolerance/stability; real-time neural decoding