Neuroprosthetics Presentation 2 Implant Technologies

Implantation Technologies Types of Augmentation technologies –Restorative- restore lost functions and replace lost organs and limbs –Normalising- restore some creature to indistinguishable normality –Reconfiguring- creating post-human creatures equal to but different from humans –Enhancing- the aim of most military / industrial research

Invasive vs. Non-invasive Restorative Application

Nervous 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 Tissue Multipolar (motor function or within the CNS), Bipolar (sensory e.g. retina), Unipolar (sensory), Pyrimidal (within the brain only) The axon from a single nerve cell is sometimes referred to as a nerve fibre, and can be over a meter in length The axon from a single nerve cell is sometimes referred to as a nerve fibre, and can be over a meter in length Many nerve fibres stream together to form a nerve or nerve fascicle - several fascicles may then coalesce to form a larger nerve trunk Many nerve fibres stream together to form a nerve or nerve fascicle - several fascicles may then coalesce to form a larger nerve trunk A nerve contains several tens of thousands of single nerve fibres of different diameters typically between 2 and 20 µm A nerve contains several tens of thousands of single nerve fibres of different diameters typically between 2 and 20 µm

Nerve Tissue Nerves have three distinct connective tissue “coats”: The epineurium is the outermost sheath of a nerve fascicle and consists of dense connective tissue. It also fills the spaces in-between the nerve fascicles and acts as a “highway” for capillaries and veins to enter the nerve The epineurium is the outermost sheath of a nerve fascicle and consists of dense connective tissue. It also fills the spaces in-between the nerve fascicles and acts as a “highway” for capillaries and veins to enter the nerve A perineurium surrounds each nerve fascicle and consists of several concentric layers of flattened cells. These cells are joined together laterally by tight junctions which serve as a diffusion barrier to larger molecules A perineurium surrounds each nerve fascicle and consists of several concentric layers of flattened cells. These cells are joined together laterally by tight junctions which serve as a diffusion barrier to larger molecules The endoneurium is found within the nerve fascicle and consists of a thin matrix of fibres which surround the axon cylinders The endoneurium is found within the nerve fascicle and consists of a thin matrix of fibres which surround the axon cylinders

Neuroprosthesis

Neuroprosthesis

Neurons 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

Neurons 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

Neurons 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 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 Communication Action 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 Neurons Functional Electrical Stimulation (FES) Functional Electrical Stimulation (FES) –Artificial stimulation of Efferent Neurons e.g.: Stimulation of the sacral roots for bladder function e.g.: Stimulation of the sacral roots for bladder function Hand grasp for tetraplegic patients Hand grasp for tetraplegic patients Ambulation for paraplegic individuals Ambulation for paraplegic individuals Sensory electrical stimulation Sensory electrical stimulation –Artificial stimulation of Afferent Neurons e.g.: Cochlear implants e.g.: Cochlear implants Taste / Smell / Vision / Touch... Taste / Smell / Vision / Touch... Example: Closed-loop ambulation control using natural sensors (i.e. glabrous skin mechanoreceptors) (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 µm long Inserted into the nerve tissue during open surgery Electrodes (intraneural)

Signal Processing

Implementation Fully implanted vs External?