Cognitive Neuroscience Lecture 6: Guest Lecture: Neuroprosthetics

*L6: Guest Lecture—Neuroprosthetics*

Recreating
sight in blind patients; case study

Inspired by
cochlear implant

Four
opportunities along visual pathway: Retina, optic nerve, LGN, Visual cortex

Outer
retinal degeneration: fewer retinal cells--Retinitis pigmentosa

So,
we put a subretinal implant in the area of loss of rods and cones

Or,
we put an epiretinal implant (easier for surgeon)

Retinal
implants started at wilmer

Small
probe in the eye

Held
by surgeon, stimulates retinal cells

Patient
awake; local anesthesia

New
epiretinal approach: argus II retinal prosthesis system

Electrodes
individually adjusted

6x10
retinal implants

Res
525 Mm

Camera,
transmitter coil, video processing unit, electronics case, receiver coil

Many
countries all over the world

Implant
approved in Europe: Alpha IMS

Electrodes
jointly adjusted

Res
80 Mm

Future:
subretinal implant

Emphasis
on extraocular transmission and processing away from stim site

Receiver
coil and electronics on temporal sclera

Scleral
tunnel to subretinal location

Future:
German Epi-Ret projects—epiretinal implants

External
camera

Wireless
transmission

Antenna
and electronics in the capsular bag

Stanford
Optoelectronic Retinal Prosthesis Concept

Subretinal
implant inducing retinal migration

US DoE
Artificial Retina project

Novel
electrode materials and light capture

Many
types of electrode arrays

Light-to
energy conversion using plant photosynthetic molecule PS II and genetic
engineering

Neurotransmitter
based retinal prosthesis (concept only, not real yet)

NT
release targets inner retina

Specific
pathway (on only or off only) excitation might be possible

Stim
through microfluidic channels in chip

Testing
in isolated retina prep

Optic nerve prosthesis

Emphasis
on processing crude info

Electrodes
in cuff around optic nerve; light/dark/direction/stim strength must be learned

Penetrating
electrodes being developed

Concept of
cortical prosthesis:

video
encoder in glasses, electrode array in V1, transcranial interconnect in base of
head, signal processor far below

Intracortical
approach: NINDS, 1992

coil,
ceramic, AIROF electrodes, counter + reference

Cortical
complication: Scrambled map

electrodes
à retinal percept?

Cortical
percept magnification isn’t exactly in order

Near future:
other active groups; human trials many years away

Planning for
prosthetics: Simulations

Where
did SSMP get the idea for 16 and 60 electrodes

First
systematic explorations through simulation

Principal
fields of investigation:

o
Wayfinding/orientation
& mobility

o
Visual
acuity/reading

o
Face
recognition

o
Hand/eye
coordination (visually guided action)

Many
stim are woefully simplistic (crisp round dots) or needlessly hard (eccentric
pixelized reading)

Route
planning in real world

Pros

o
Easy
to create

o
Useful
for early trials

Cons

o
Layout
quickly learned

o
Unnatural
(why do that if cane/dog works just as well)

o
Potential
risk

Real-world
wayfinding: results

Sighted
subjects trained on pixelized viewing

Fast
usually = sloppy

High
res is better but not perfect

6
x 10 good enough

Hurdles for
implant wearers: Stabilized view

Stabilized
view

o
Needed
because eye movement is a lot of extraneous movement

o
Subjects
learn to hold eyes still

o
Subjects
learn to move camera

**Modeling prosthetic vision in a**
nutshell

Filter
software transforms camera image or virtual scene

Eye-tracking
stabilizes raster location (optional)

Subject
views scene in headset (monocularity)

Eye-head-hand
coordination

Virtual
mobility

Dots
locked to eye position

Hurdles for
implant wearers: Spatial filtering

Prosthetic
vision in the operating room

Stim
single electrodes (retina or cortex): perceived in correct location, flicker
perceived up to 40hz

Stim
multiple electrodes (mostly retina): crude shape scene (single row/col),
blurrier than dots, hard to see flicker

Retinal
rewiring: inner nuclear layer cells migrate and form clusters

Meander
mazes; maze tracing

Hurdles for
implant wearers: Temporal filtering

Maze
tracing, temporal low-pass filter

Hurdles for
implant wearers: Spontaneous bg activity

All
prostheses, even ideal ones, give light shows

Argus II:
moving shadows

prosthetic
!= normal

Lots of
training needed

Performs
line task better than without it

Finding
objects and seeing movement: Square localization/direction of motion

Spot
reading and object recognition

Orientation
and mobility