Optimizing Gait Rehabilitation: How Can Nervous System Plasticity
Be Harnessed? Jesse Dean
3.24.10
Introduction
• Restoration of functional mobility is a high ranking goal
• Neurological injuries commonly limit independent locomotion– Stroke: 800,00 per year– Spinal cord injury: 12,000 per year
(Anderson, 2004)
Gait rehabilitation can improve function
Therapist-Assisted Powered Exoskeletons
•By moving the legs through walking-like motions, patients can “relearn” how to walk
•Treadmill training improves muscle activation patterns (Dietz et al., 1994), gait speed, and gait symmetry (Field-Fote, 2000)
(Fritz et al., 2007) (Dietz et al., 1995)
Recovery is due to neural plasticity
• Nervous system connections are not hard-wired
Recovery is due to neural plasticity
• Nervous system connections are not hard-wired– Multiple paths from one point to
another
Recovery is due to neural plasticity
• Nervous system connections are not hard-wired– Multiple paths from one point to
another
• Activity-dependent plasticity may create functionally relevant new connections– “Fire together, wire together”
Promoting plasticity for gait recovery
To form/strengthen new functional circuits:A)Descending commands must be present
Promoting plasticity for gait recovery
To form/strengthen new functional circuits:A)Descending commands must be presentB)Motor pools must be recruited at appropriate times
Promoting plasticity for gait recovery
To form/strengthen new functional circuits:A)Descending commands must be presentB)Motor pools must be recruited at appropriate timesC)Muscle contractions must drive movement, eliciting sensory feedback
Proposed Interventions
• Mechanical
• Physiological
To form/strengthen new functional circuits:A)Descending commands must be presentB)Motor pools must be recruited at appropriate timesC)Muscle contractions must drive movement, eliciting sensory feedback
Proposed Interventions• Mechanical– Goal: Drive walking
motion with reduced muscle activation
– Method: Use the principles of dynamic walking to essentially make walking easier
• Physiological
To form/strengthen new functional circuits:A)Descending commands must be presentB)Motor pools must be recruited at appropriate timesC)Muscle contractions must drive movement, eliciting sensory feedback
Mechanical Intervention: Passive Exoskeleton
• Based on previous mechanical model simulations
• Appropriate spring placement– Reduces energetic cost
by ~10%– Reduces swing phase
muscle activity by up to 40%
(Dean, 2009)
Proposed Interventions
• Mechanical
• Physiological
To form/strengthen new functional circuits:A)Descending commands must be presentB)Motor pools must be recruited at appropriate timesC)Muscle contractions must drive movement, eliciting sensory feedback
Proposed Interventions• Mechanical
• Physiological– Goal: Promote
appropriate motor neuron firing in response to decreased excitatory input
– Method: Increase excitability through motor neuron intrinsic properties
To form/strengthen new functional circuits:A)Descending commands must be presentB)Motor pools must be recruited at appropriate timesC)Muscle contractions must drive movement, eliciting sensory feedback
Peripheral electrical stimulation can modulate motor pool excitability
• Non-invasive stimulation over a muscle or nerve:– Causes recruitment and continued activation of homonymous motor
pool– Inhibits recruitment of the antagonist motor pool
• Likely due to modulation of persistent inward currents, an intrinsic property of neurons
(Dean et al., 2008)
Motor pool modulation during gait may promote plasticity
• Increased excitability will allow motor pool recruitment with weaker descending commands (thus strengthening connections)
• Decreased excitability will prevent strengthening of non-functional connections
(Hof et al., 2002)
Stimulation can be driven by mechanical feedback
• May be used either in combination with or independent from mechanical intervention
(Hof et al., 2002)
Conclusions
• Gait rehabilitation outcomes may be improved through neural plasticity by:– Mechanical interventions allowing residual control to
power walking– Physiological interventions promoting appropriately
timed motor pool recruitment• Anticipated issues:– Ability of non-invasive techniques to form neural
connections is limited– Application of these ideas to clinical populations
Optimizing Gait Rehabilitation: How Can Nervous System Plasticity
Be Harnessed? Jesse Dean
3.24.10
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