Illusion of arm movement evoked by tendon vibration in patients with spinal cord injury

Background: Studies in healthy people show that stimulation of muscle spindles through frequency-specific tendon vibration (TV) induces the illusory perception of movement. Following spinal cord injury (SCI), motor and sensory connections between the brain and parts of the body below-the-lesion level are partially or totally impaired. Objective: The present investigation is a descriptive study aimed to investigate whether people living with SCI may experience movement illusions comparable to a control group. Methods: Healthy and people with SCI were asked to report on three illusion-related features (Vividness, Duration, Illusory Extension) after receiving 70Hz TV on the biceps brachii tendon of both arms. Two different forces of stimulation were applied: 2.4N and 4.2N. Results: Both patients and controls were susceptible to the kinesthetic illusion. However patients presented lower sensitivity to TV than healthy subjects. Participants rated stronger illusions of movement after 4.2N than 2.4N stimulation in all the three illusion-related features. Further, patients reported atypical illusory experiences of movement (e.g. as if the arm wanted to extend, or a sensation of pushing against something) that may reflect different reorganization processes following spinal cord injury. Conclusion: The study provides a preliminary evidence of the possible use of the proprioceptive stimulation in the upper limbs of people living with SCI. Results are discussed in the light of recent advancements of brain-computer applications based on motor imagery for the control of neuroprosthetic and robotic devices in patients with severe sensorimotor deficits.