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