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Brain and Spinal Cord Machine Interfaces: A View from the Clinical Edge

Brain and Spinal Cord Machine Interfaces: A View from the Clinical Edge. Peter Konrad, MD PhD Assoc Professor Neurosurgery and Biomedical Engineering Vanderbilt University. Dr. Konrad has no financial disclosures relevant to this talk

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Brain and Spinal Cord Machine Interfaces: A View from the Clinical Edge

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  1. Brain and Spinal Cord Machine Interfaces:A View from the Clinical Edge Peter Konrad, MD PhD Assoc Professor Neurosurgery and Biomedical Engineering Vanderbilt University

  2. Dr. Konrad has no financial disclosures relevant to this talk There is discussion of the use of FDA-approved devices in off-label applications

  3. Emergence of Extrinsic Neurally Controlled Systems • Goals: • Restore lost motor fxn • Restore lost sensory fxn • Restore internal control signals • Examples: • Parastep FES • Cochlear prosthesis • ITB / Bladder prosthesis Stroke Motor Signal Extraction SCI Sensory Signal Insertion ALS Amputation

  4. Neuromodulation in Disability • Brain: • Extract unique cortical signals • Insert lost sensory information • Spinal cord: • Cervical region: Hand function / UE limb sensation • Lumbar enlargement: Standing, walking, B/B ctrl • Spasticity control • Peripheral nerves: • Focal deficit: amputation, peripheral injury

  5. Brain Machine Interface: Cortex • Advantage: • Unique cortical sensori-motor experience • Anatomically well defined regions • Access relatively easy • Tolerant of implantation (?) • Disadvantage: • Coding of information highly complex • Sensory plasticity • Potential seizures with some types of chronic stimulation

  6. Physiology of Motor Coding • Human studies show potential for motor signal extraction real time • Thalamic micro-wire implants (Patil et al 2004) • Cortical Utah array in quadriplegic (Hochberg et al 2006) • Able to move screen cursor • >5 years implanted

  7. Physiology of Motor Coding • Visual cues are integral to closed-loop BMI control • Speed of processing circuitry important in a functional BMI unit • Shenoy et al: 4 words/min • Volitional control will require significant number of channels and processor speeds

  8. BMI for Sensory Control • Sensory experience easily dissipates / plasticity • Role of BMI Less understood Sadato et al. Neurosci Lett 2004

  9. BMI for Sensory Input:State of Technology • Auditory prosthesis represent most extensive clinical impact of BMI • Better response with more centralized implant • Present ABI since 1993 • 21 electrodes OK for speech recognition Lenarz et al. Otol Neurotol 2006

  10. Spinal Cord Machine Interface • Advantage: • Injury affects a segment of cord • Regionally specific function (cervical, thoracic, lumbar) • Integration sensori-motor function already in place • Plasticity not known • Disadvantage: • Anatomy very compact • Surgically more risky • Not well suited for subtle, volitional control

  11. SCMI: ITB for adjustment of reflex tone • Spasticity: • Hypertonicity of AMN • Baclofen (GABAb) replaces lost regulation • ITB therapy: example of SCMI • Simple system at present • Likely to be a significant adjunct to other SCMI From Brain GABA

  12. Organization of Spinal Cord SENSORY • Motor: • Anterior horn • Motor tracts (5) • Sensory: • Posterior horn • Sensory tracts (3) • Autonomic: • Intermediate gray • Sympathetic tracts T1-T12 • Parasympathetic S2-5 MOTOR AUTONOMIC

  13. Physiological Organization of the Spinal Cord • Central Pattern Generators (CPGs) • Standing: Extensor tone predominates (reticulospinal system) • Walking: recipricol Flex / ext activity • Balance: Agonist-antagonist reflex (vestibulospinal system)

  14. Motor Control in the Spinal Cord

  15. Spinal Cord AMN Pools during stepping in normal cat Yakovenko S et al. J Neurophysiol 2002;87:1542-1553.

  16. Motor Spinal Cord Machine Interface • Concept is to discretely activate AMN pools (30-60µA; 200µsec) • Can accomplish standing and walking through separate stim points (est 2X4=8) • Standing: > 20 min body weight (vs 4 min with IMS) • Walking: > 140 steps (>200m) • Implants: 67% functioning at 6 months CATS Mushahwar et al. J Neural Eng 2007

  17. Motor Spinal Cord Machine Interface FES Muscular stim in a complete paraplegic ISMS in complete paraplegic cat

  18. Motor Spinal Cord Machine Interface • Epidural stimulation can also initiate stepping patterns • Based on FRA stimulation studied in 1911 by Graham Brown

  19. Motor Spinal Cord Machine Interface • L2-3 cord (T12 vert) stim • Non-weight bearing patients • Stepping patterns only generated • Rehab potential is large for this therapy (maintain muscle tone at a minimum) Q H TA TS KM vertical markers: 500 µV (EMG), 45° (goniometer); horizontal marker: 1 s (time) (7V-10V) Minnassian et al. Spinal Cord 2004

  20. Sensory Insertion into the Spinal Cord • Cordotomies - SC stim tolerated in awake humans • ALST: pain, temp • DCLS: mechanical, vibration, proprioception L

  21. Sensory Insertion into the Spinal Cord ? USEA Konrad, Diedrich et al. Vanderbilt Univ (unpublished data)

  22. Autonomic SC Machine Interface Arch Surg 1972;104:195-202

  23. The Bigger Picture • Bridging a Lesion: • Brain : Peripheral Nerve • Brain : Spinal Cord • Spinal Cord : Peripheral Nerve • Spinal Cord contains Viable lnterface Options for Neuroprosthetics Stroke Motor Signal Extraction SCI Sensory Signal Insertion ALS Amputation

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