kyiv public presentation · pu ˆoses of neu l inte aces • instruments generally perform the...

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Kyiv Public Presentation:

The State of the Art in

Neural Interfaces

Dan Merrill PhD

3 November 2016

Outline

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• What is a neural interface?

• Organization of the nervous system

• Applications of neural interfaces

• Success stories

• Two primary objectives: Effectiveness and safety

• Peripheral and central interfaces

• Specific devices used as neural interfaces

• What is the future? Risks and ethical considerations

What is a Neural Interface?

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A neural interface is an engineered

(man-made) device which connects to

the human nervous system, for the

purpose of augmenting, replacing or

repairing nervous system functions

which have been degraded or lost.

Organization of the Nervous System

• Sensory organs � processing � output to muscles and glands

• Central nervous system (CNS): The brain and spinal cord

• The human brain contains between 80 and 90 billion neurons

• Peripheral nervous system (PNS): Neurons outside of the CNS

• The PNS can be divided into divisions both structurally and functionally

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The Neuron

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Cell body:

20 to 100 μm dia.

Axon:

0.1 to 10 μm dia.

Up to 1 meter long

Neurons carry information,

one to another,

like links in a chain

Brain Structure

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Coronal (front to back) plane

Sagittal (left to right) plane

Gray matter / cerebral cortex

Unmyelinated cell bodies

Only ~ 2 - 4 mm thick

White matter

Myelinated axons

Human brain facts:

3 lbs

1,100 – 1,500 cc

80 - 90 billion neurons

Applications of Neural Interfaces

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Foot Drop

Facial Palsy

Dysphagia

Cerebral Palsy: Spasticity

Spinal Cord Injury: Respiration, Cough

Arm Rehabilitation

Incontinence, Sexual Function

Gait Rehabilitation

Stroke,Traumatic Brain Injury

Pressure Ulcers

Nerve Repairand Regrowth

Amputation

Bioelectric Medicine / Electroceuticals: Trading Drugs for Devices

Worldwide:

• Diabetes: 1/3 billion

• Obesity: 3/4 billion

• Hypertension: >1 billion

• Cardiovascular disease:

31% of all deaths globally

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The autonomic nervous system controlling the chest, gut, blood vessels

Purposes of Neural Interfaces

• Functional Electrical Stimulation (FES) is electrical stimulation of nerves or muscles in order to cause coordinated muscle contraction, yielding immediate replacement or augmentation of lost or degraded function

• Therapeutic Electrical Stimulation (TES) is intended to assist in long-term repair of the body, by

• inducing neural plasticity (the ability of the nervous system to change),

• development of alternative control pathways,

• muscle strengthening, or stretching of spastic muscles 9


• Implanted devices are placed inside the body

• External devices have electronics placed outside the body (usually sitting on top of the skin), and may be either

• Transcutaneous: all parts of the device are outside the body, including electrodes which sense or stimulate

• Percutaneous: electronics are outside the body, and a lead wire passes through the skin to electrodes inside the body

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• Instruments generally perform the functions of observing and controlling

• In the context of a neural interface, these are called sensing and stimulating

• A sensing interface records the electrical activity which is occurring in the nervous system

• A stimulating interface generates electrical signals in the nervous system

• If we stimulate a sensory neuron, a person may perceive a sensation

• If we stimulate a motor neuron, muscle contraction may occur 11

An Example of Sensing and Stimulating

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Success Story 1: Restoration of Sensation / Clark Lab

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Virtual door with

handle

Decode of muscle signals

enables movement of

digits and wrist

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Sensation via USEA

stimulation

Success Story 1 / Clark Lab

Success Story 2: Prosthesis Control, with Sensation / Tyler Lab

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Success Story 2: Prosthesis Control, with Sensation / Tyler Lab

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Success Story 3: Treatment of Parkinson’s Disease

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Targets within the brain for movement disorders: • Subthalamic nucleus (STN)• Thalamus• Globus pallidus (GPi)

Success Story 3: Treatment of Parkinson’s Disease

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Effectiveness and Safety

The two primary objectives for a medical device, or medicine, are:

• Effectiveness: achieving the desired response

• Safety: not causing damage

These are sometimes contradictory objectives. An invasive implanted device, which is generally riskier than an external device, often gives better performance

A culture is defined by the balance point between effectiveness and safety

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Specific Objectives

Stimulation devices

• Effective

• Deliver enough charge to cause the desired response

• Reliable: Properties are stable over intended device lifetime

• Safe

• No chemical reactions causing damage to tissue or device

• Biocompatible: Device doesn’t damage tissue, and vice versa

Recording devices

• Effective

• Sensitive: Records small signals of interest

• Selective: Doesn’t record the wrong signals

• Reliable: Properties are stable over intended device lifetime

• Safe: Passive device is biocompatible 20

Smaller is Better

21Joe Schulman, ca.1963

Smaller is Better

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Integrated circuit of the Bion implanable stimulator: 1.07 mm x 5.49

mm, and contains the equivalent of 20,000 transistors

Central and Peripheral Interfaces

Central interfaces connect with the brain or spinal cord

• More invasive, more risky

Peripheral interfaces connect with nerves

• Less invasive, less risky

23Central InterfacesPeripheral

Interfaces FINE

USEA

USEA

DBS ECoG

Effectiveness and Safety:Recording from the Brain

Scalp EEG

• Selectivity: 6 to 8 cm3

• Sensitivity: Amplitudes 10 to 100 μV

• Invasiveness: Minimal

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Scalp EEG




Penetrating Microelectrodes

• Selectivity: Less than 1 mm3

• Sensitivity: Up to a few mV

• Invasiveness: Highly25


Scalp EEG




Subdural Electrocorticography

• Selectivity: Less than 1 cm3

• Sensitivity: Up to hundreds of μV

• Invasiveness: Moderate

Penetrating Microelectrodes

• Selectivity: Less than 1 mm3

• Sensitivity: Up to a few mV

• Invasiveness: Highly26

Effectiveness and Safety:Recording from Muscle

Surface Electromyogram (EMG)

• Selectivity: Modest

• Sensitivity: Modest

• Prosthesis performance:

Sequential control


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Intramuscular EMG

• Selectivity: Excellent

• Sensitivity: Excellent

• Prosthesis performance:

Simultaneous multiple

degree-of-freedom control

• Invasiveness: Moderate Myoelectric Implant

Technologies of the Future (?)

Material interfaces with mechanical properties

like human tissue: Thin, flexible electrodes

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Organic devices that self-integrate into tissue

Small, high-channel count electrodes �

allows study of complex neural networks

Risks and Ethical Considerations

• Who decides the balance of effectiveness vs. safety? The patient? The government?

• How do expensive, complex devices get fairly partitioned into society?

• Who pays? Class stratification?

• Memory replacement

• In early stages of development, but it is coming

• When does the sense of self change? If I receive another person’s memories, or fabricated memories, am I still me?

• Replacement of lost function vs. augmentation

• Will we create a super-class of humans? Who chooses? The wealthy? The powerful? The government? 29

ДУЖЕ ТОБI ДЯКУЮ

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