Neuroplasticity induced by functional electrical stimulation

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Compromised standing and walking function among people who have paralyzed muscles due to a neurological disease or injury, such as spinal cord injury or stroke, critically limits their ability to perform activities of daily living, and reduces their quality of life. Functional electrical stimulation, which is a method that can artificially activate muscles in the paralyzed limbs by use of electrical stimulation, can lead to improvement of patient’s affected limb function. For example, when a person with a paralyzed arm needs to grasp a coffee cup, muscles that close fingers are stimulated to produce a grasping movement. This is an effective way to regain functional movements, but it is practically difficult to apply to many complex movements which are required during activities of daily living. It was discovered that repetitive use of functional electrical stimulation can cause permanent changes of the neural circuits in the brain and/or the spinal cord, which is the so-called neuroplasticity. This discovery could have tremendous impacts in neurorehabiliation but the neural mechanisms and the effective ways of using functional electrical stimulation to induce the neuroplasticity are not fully understood. One probable mechanism behind the neuroplasticity induced by functional electrical stimulation is the synaptic strengthening at the spinal cord. When a command from brain and the signal caused by electrical stimulation which is traveling backward on the motor nerve meet at spinal cord, the strength of the synaptic connection between the brain and the muscle increases (i.e., how effectively the command from brain travels to muscle). Repeating this process leads to permanent strengthening of the connection between the brain and the muscle, which can increase the muscle force and improve limb movement. The proposed research program aims to explore the effective ways that functional electrical stimulation can facilitate neuroplasticity in the human motor control system, focusing on this synaptic strengthening at the spinal cord, i.e., what is happening in the spinal cord. For this mechanism, two neural signals are required: One from the brain and the other from peripheral nerves. A signal from the brain can be induced simply by the patient’s voluntary effort (i.e., if patient want to move a limb, a command from brain will travel to the muscle). The other way to cause a signal from the brain is to use transcranial magnetic stimulation. By stimulating the cortical area of the brain responsible for the limb moment, transcranial magnetic stimulation activates the responsible neurons and the neurons send a command to the muscle. There are four ways to cause the neural signal from peripheral nerves; 1) to stimulate the sensory nerve trunk at a nerve pass to the target muscle, 2) to stimulate the nerve ending within the target muscle, 3) to stimulate the motor neurons in the spinal cord, 4) to stimulate the motor nerve trunk at a nerve pass to the target muscle. By appropriately combining the brain neural signal and neural signal from peripheral nerves, it is hypothesized that neuroplasticity can be induced at the spinal cord. In this program, I will test each combination systematically to investigate and develop the most effective way to deliver functional electrical stimulation to induce the synaptic strengthening between the brain and the muscle. At the end, this program will develop a basis of a neuroengineering method which can help people with paralyzed muscles regain their lost movements, which will inevitably lead to increased quality of life.