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Neural Prosthetic: Mind Reading.
STATS 19 SEM 2. 263057202. Talk 6.
Alan L. Yuille.
UCLA. Dept. Statistics and Psychology.
www.stat.ucla/~yuille
Neural Prosthetic.
• Basic Idea:
• Injury to spinal cord
prevents actions.
• But patient can still
think, or plan, the
actions.
• If these plans can be
decoded by a
microchip, then the
patient can control a
robot limb, or other
device.
Mind Reading.
• Basic Assumption: Mind = Brain.
• Brain consists of neurons transmitting
information by electrical activity.
• All thoughts have neuronal correlates.
• If you can decode the activity of neurons, then
you can read people’s thoughts.
Neural Activity
• Decoding neural activity corresponds to mind
reading.
• But how do neurons encode information?
• Two classic viewpoints:
1. The grandmother cell that responds whenever
you see your grandmother.
2. Activity encoded by populations of neurons.
Neural networks (holistic).
Decoding Neurons.
• It seems clear that some brain activity is
localized in specific areas – e.g. face
recognition.
• Also some neurons respond to specific
stimuli – e.g. to faces but not to dogs.
• There might even be a Clinton cell…
• There is a lot of plasticity.
Motion Planning
• Motion Planning : experiments (1990)
showed that populations of neurons in the
motor cortex predicted the direction of
movement.
• Better ways to interpret neuronal activity –
get monkeys to perform simple tasks,
measure neuronal activity, perform
Bayesian inference. (Brown University).
Plasticity and Feedback Helps
• The decoding is used to drive a device.
• The monkey gets feedback by observing
that the device is not doing what it
wanted.
• The monkey can somehow correct its
thought patterns, so that the decoding
works.
• Like learning to ride a bicycle.
Movement Planning
• These movement plans, or thoughts, need
not be conscious.
• Novel actions usually require conscious
thought.
• But most common actions do not.
• Neuronal correlates of consciousness.
Neural Prosthetics.
• Only a few Universities have serious neural
prosthetics programs.
• This talk describes work by Richard Andersen’s
Laboratory at Caltech. Figures copied from the
lab’s webpage.
• Michael Black at Brown University. (Decoding).
Goal of Neural Prosthetic System.
• Read the
•
plans
from the
cortex.
Activate
an
external
device.
Implanting Electrodes.
• Measurement is done by
•
•
inserting electrodes into
the cortex. These
transmit to an external
device.
Will the implanted
electrodes stay in the
right place? Will they
cease functioning over
time?
But the electrodes only
need to measure activity
(passive). They do not
need to stimulate
neurons (epilepsy).
How to Implant Electrodes?
• Neurosurgery:
• Deep implants of
•
electrodes to simulate
(treatment for
Parkinson’s disease).
No pain receptors in
the brain.
Miniaturized Chip.
• Chip must measure
•
neuronal activity.
Action potentials.
Where the Output Goes.
• Chip implanted
inside the brain.
• Wires go out and
activate external
devices.
Posterior Parietal Cortex.
• Earliest place where the
thought to make a
movement is made.
• Size of little fingernail.
• About 50,000,000
neurons.
• Others work with motor
cortex. But this can
atrophy with disuse.
Plans made in PPC. Sent to Motor Cortex.
Transmitted to Spinal Cord.
Cognitive Plans
• Planning and
Visual
Coordinates.
• Advantage of
PPT.
Parietal Reach Region.
• Reach,
Move
Eyes,
Grasp.
Spatial Representation Known.
• Knowing spatial representations makes it
easier to read the neuronal code.
Neural activity as Monkey Thinks.
• Monkey is
•
trained to
perform
tasks.
Waiting
period
when
monkey
plans.
Close the Loop by Giving Feedback.
• Monkey has
•
feedback.
Monkey can
adjust neural
activity to
improve
performance.
Improve Recordings.
• Moveable Probe
• Need to adjust
Electrodes to take
tissue movement
into account.
Computer Probe.
• Adjust Probes.
• 1,000 electrodes.
Automatically
optimize positions.
• Microfluidic drug
delivery. To remove
scar tissue.
Decoding Neural Activity.
• Local Field
Potentials.
Local Field Potentials.
• Measure Field
Potentials.
Tuning of Local Field Potentials.
• Local Field Potentials:
Decoding LFP’s and Spikes
• Decoding.
Informatics.
• Real Time Decoding.
• Analysis is similar to that for speech
•
•
recognition.
Information in space and time.
Similar techniques can be used.
Summary.
• Planned movements are represented in
the Parietal Reach Region.
• Neural decoding enables these plans to be
read.
• Plasticity of neurons makes this easier,
training by feedback.
• Implanting device by deep brain surgery.
• Output wires control external device.