Muscle Spindles and Our Sense of Physical Self: Kinesthetic Illusions of Limb Position and Posture.

This article describes three simple activities we presented at the 2017 FUN Faculty Workshop at Dominican University that demonstrate how proprioceptive information contributes to our mental image of physical self, and how artificially altering this information creates kinesthetic illusions. We focus on the muscle spindle contribution to limb positional sense and standing postural maintenance. We use a percussion stimulator to vibrate muscle spindles in several muscle groups, causing an artificially incorrect message to the CNS that a muscle has lengthened. This creates an illusion of limb position or standing posture change. Although descriptive data can suffice to engage students in these activities, we suggest quantitative measurements to add further depth. These activities are open for continued student-designed exploration. They lead directly to discussions of sensory physiology, central pathways for integration of sensory information and spinal pathways to execute motor commands. A broader context for the activities could include postural adaptations at sea and upon return to land, postural illusions experienced by astronauts and the postural and locomotor problems they experience upon return to Earth, and the effects of aging and disease on the proprioceptive control of limb position and posture.