Preliminary electrophysiological characterization of functionally vestigial muscles of the head: potential for command signaling.

In devastating neurological disorders, such as quadriplegia resulting from high-level spinal cord injury, it is essential to focus on functions that have been spared and optimally exploit them to enhance the individual's quality of life. It follows that certain muscles, which prior to the paralysis of much of the rest of the body seemed to have no useful function, might be used to provide unique signals to control assistive devices. This report presents preliminary electrophysiological data demonstrating potentially useful myoelectrical signals from 3 functionally vestigial muscles in humans; the posterior, anterior, and superior auricular muscles. In phylogenetically lower species, these muscles serve to position the ear to enhance hearing. The auricular muscles receive their major innervation from cranial nerve VII and should not be compromised by even high-level spinal cord lesions. In this study, it was found that the muscles could be voluntarily activated and, by standard surface-electrode recording, had potentials ranging to 680 microV in amplitude. Posterior auricular muscle potentials were used to command a paddle in a computer ping-pong task that employed a CyberLink interface. The t values for accuracy scores and ball hits were both significant at the p = .0001 level. These facts indicate that the auricular muscles may be useful for controlling assistive devices.