Neuroprosthetics Neuroprosthetics

Presentation 2Presentation 2

Implant TechnologiesImplant Technologies

Implantation TechnologiesImplantation Technologies

Types of Augmentation technologiesTypes of Augmentation technologies

– RestorativeRestorative- restore lost functions and - restore lost functions and replace lost organs and limbsreplace lost organs and limbs

– NormalisingNormalising- restore some creature to - restore some creature to indistinguishable normalityindistinguishable normality

– ReconfiguringReconfiguring- creating post-human - creating post-human creatures equal to but different from creatures equal to but different from humanshumans

– EnhancingEnhancing- the aim of most military / - the aim of most military / industrial researchindustrial research

Invasive vs. Non-invasive

Restorative ApplicationRestorative Application

Nervous SystemNervous System

The basic unit of the nervous system is the neuron, or nerve cell, which transmits signals between the CNS and receptors (senses) and effectors (muscles, glands, etc) in other parts of the body

Nerve TissueNerve Tissue

Multipolar (motor function or within the CNS), Bipolar (sensory e.g. retina), Multipolar (motor function or within the CNS), Bipolar (sensory e.g. retina), Unipolar (sensory), Pyrimidal (within the brain only)Unipolar (sensory), Pyrimidal (within the brain only)

• The axon from a single nerve cell is sometimes referred to as a The axon from a single nerve cell is sometimes referred to as a nerve fibrenerve fibre, and can be over a meter in length, and can be over a meter in length

• Many nerve fibres stream together to form a Many nerve fibres stream together to form a nervenerve or or nerve fasciclenerve fascicle - several fascicles may then coalesce to form a larger - several fascicles may then coalesce to form a larger nerve trunknerve trunk

• A nerve contains several tens of thousands of single nerve fibres of A nerve contains several tens of thousands of single nerve fibres of different diameters typically between 2 and 20 µmdifferent diameters typically between 2 and 20 µm

Nerve TissueNerve Tissue

Nerves have three distinct connective tissue “coats”: Nerves have three distinct connective tissue “coats”:

• The The epineuriumepineurium is the outermost sheath of a nerve fascicle and is the outermost sheath of a nerve fascicle and consists of dense connective tissue. It also fills the spaces in-consists of dense connective tissue. It also fills the spaces in-between the nerve fascicles and acts as a “highway” for between the nerve fascicles and acts as a “highway” for capillaries and veins to enter the nervecapillaries and veins to enter the nerve

• A A perineuriumperineurium surrounds each nerve fascicle and consists of surrounds each nerve fascicle and consists of several concentric layers of flattened cells. These cells are several concentric layers of flattened cells. These cells are joined together laterally by tight junctions which serve as a joined together laterally by tight junctions which serve as a diffusion barrier to larger moleculesdiffusion barrier to larger molecules

• The The endoneuriumendoneurium is found within the nerve fascicle and consists is found within the nerve fascicle and consists of a thin matrix of fibres which surround the axon cylindersof a thin matrix of fibres which surround the axon cylinders

NeuroprosthesisNeuroprosthesis

NeuroprosthesisNeuroprosthesis

NeuronsNeurons

Three functional classes of Neuron:

Afferent Neurons:

• Transmit information into the CNS from receptors at their peripheral endings

• The cell body and axon is outside the CNS

• They have NO dendrites

NeuronsNeurons

Three functional classes of Neuron:

Interneurons:

• Integrate groups of afferent and efferent neurons into reflex circuits

• Are entirely within the CNS

• Account for 99% of all neurons

NeuronsNeurons

Three functional classes of Neuron:

Efferent Neurons:

• Transmit information out of the CNS to effector cells

• The cell body and dendrites are inside the CNS

• The axon is outside the CNS

Efferent NeuronsEfferent Neurons

Efferent neurons are subdivided:

Somatic Nervous System: Made up of all the nerve fibres going from the CNS to skeletal-muscle cells

Autonomic Nervous System: The efferent innervation of all tissues other than the skeletal muscle

Because activity in the somatic neurons leads to contraction of the innervated skeletal muscle cells, these

neurons are called ‘Motor Neurons’

Nerve CommunicationNerve CommunicationAction Potentials:

Central to all nervous systems are the ‘action potentials’, nerve signals that are generated in

response to stimuli or to control motor units

When a neuron is not being stimulated, it is at its Resting Potential

If a sudden rise pushes the membrane potential above the Threshold Value, (usually ~ 55mV), depolarisation spontaneously occurs (Initiation) and an action potential is generated

Action potentials occur maximally or not at all (All-or-None Response)

Under normal conditions the duration and magnitude is always the same

• Recording of neural activity Recording of neural activity – From Afferent or Efferent NeuronsFrom Afferent or Efferent Neurons

• Functional Electrical Stimulation (FES)Functional Electrical Stimulation (FES)– Artificial stimulation of Efferent NeuronsArtificial stimulation of Efferent Neurons

• e.g.: e.g.: Stimulation of the sacral roots for bladder functionStimulation of the sacral roots for bladder function• Hand grasp for tetraplegic patientsHand grasp for tetraplegic patients• Ambulation for paraplegic individualsAmbulation for paraplegic individuals

• Sensory electrical stimulation Sensory electrical stimulation – Artificial stimulation of Afferent NeuronsArtificial stimulation of Afferent Neurons

• e.g.: e.g.: Cochlear implantsCochlear implants• Taste / Smell / Vision / Touch . . .Taste / Smell / Vision / Touch . . .

Example: Closed-loop ambulation control using Example: Closed-loop ambulation control using natural natural sensors (i.e. glabrous skin sensors (i.e. glabrous skin mechanoreceptors)mechanoreceptors)

(Peripheral) Neuroprosthesis(Peripheral) Neuroprosthesis

Interfacing methods: MicroElectrode Array (MEA)

This technique provides highly selective recording of individual responses of sensory and motor neurons within the nerve fascicles

Radius of electrode tip is approximately 1-3 µm. The active electrode region is approximately 50-80 µm longInserted into the nerve tissue during open surgery

Electrodes (intraneural)Electrodes (intraneural)

Signal ProcessingSignal Processing

ImplementationImplementationFully implanted vs External?