Cortical Neural Prosthetics Presented by Artie Wu

Cortical Neural Prosthetics Andrew B. Schwartz –Department of Neurobiology and Bioengineering, University of Pittsburgh –Annual Review of Neuroscience :

Outline Background on Neural Prosthetics Motivation Electrodes –Microwires –‘Michigan’ probes –Cyberkinetics probes Complications Extraction Algorithms FLAMES: Floating Light Activated Micro Electrical Stimulator

Neural Prostheses Stimulating and recording electrodes implanted in cerebral cortex to activate neurons in different parts of CNS Cortical Neural Prostheses (CNP) to control arm movement –Use neural activity to control devices to replace natural, animate movements in paralyzed individuals

Current Benefits of Neural Prostheses Restore hearing, vision Alleviate symptoms of Parkinson’s Disease (PD) Rid Tourette syndrome Mitigate head or spinal-cord trauma Restore movement in paralyzed patients

Ridding Tourette Source: University Hospitals of Cleveland, affiliated with CWRU

Problems of Muscle Activation Muscle activation muscle force is nonlinear problem Primary motor cortex drives motor activation –Depends on force, muscle length, limb geometry, orientation of limb relative to external forces, and inertia of moving segments

Representing Movement Current CNPs represent movement as end point displacements –Motor cortical discharge rate proportional to tuning function (discharge rate related to direction) All cells actively code each direction Weighted response gives specific direction using Population Vector Algorithm (PVA) Magnitude and direction of this neural vector representation is highly correlated with movement velocity

CNP: 3 Components Record neural activity –Microelectrodes and recording electrodes Extraction algorithm of neural code –Real time data acquisition and conversion to end point positions Actuators –Animated computer displays, movement of robot arm, or activation of muscle

Electrodes: Microwires First chronic recording electrodes 20-50μm diameter Optimal insertion depth uncertain

Electrodes: Silicon Micromachined Microprobes ‘Michigan’ probe –Planar devices –Boron diffusion delineates shape of probe –Multiple recording sites along shaft

Electrodes: Silicon Micromachined Microprobes Cyberkinetics Inc/University of Utah array –100 microelectrodes array on 4mm by 4mm base –Array inserted into cortex

Tissue Reactions Blood vessels disrupted and microhemorrhage Astrocytes proliferate and form encapsulation around electrode Cellular sheath around electrode with dense cells Swelling pushes neurons away Neuron density is increases after several weeks

Impedance Caused by Encapsulation Source: ‘Chronic neural recordings using silicon microelectrode arrays electrochemically deposited with a poly(3,4-ethylenedioxythiophene) (PEDOT) film’, K. Ludwig, J. Neural Eng ,

Extraction algorithms: Inferential Population Vector Algorithm relates movement direction and firing rate in motor cortex D – b o = A ·cosθ = b x m x + b y m y + b z m z D: discharge rate A: amplitude of tuning function Θ: angle between cell’s preferred direction B: vector in direction of preferred direction, magnitude is A M: unit vector in movement direction

Extraction algorithms: Classifiers Based on pattern recognition Ex: Self-organizing feature map (SOFM) –Single layer of nodes connected to input vector with set of connection weight (i.e., discharge rate) –Initially, weight vectors set randomly –Element with weight vector closest to input vector = winner –Neighbor’s weights moved closer to input vectors –Each cluster assigned direction

FLAMES: Floating Light Activated Micro Electrical Stimulators Source: Steve Menn

FLAMES: Floating Light Activated Micro Electrical Stimulators Source: Steve Menn

FLAMES: Floating Light Activated Micro Electrical Stimulators Source: Steve Menn

Round 3 Design Specs 56 different devices 1,2,3,4 diodes With and without 50kΩ parallel resistor

Thank you