Multisensory integration in kinesthesia

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Kinesthesia, the ability to accurately perceive the position and movement of the body without the aid of vision, is vital for the control of human movement. The study of this remarkable ability has had a long and interesting history. Initially, "corollary" commands from the brain, associated with the descending command to move, were thought to mediate our kinesthetic senses. Subsequently, receptors in joints held favor as the main kinesthetic input signals. Since the 1970's, however, signals from muscle spindles (length sensitive receptors in muscle) have consistently been demonstrated to provide signals that are important for kinesthesia. In more recent years, evidence has accumulated that signals from receptors in the skin also contribute. The prosed research program is designed to determine how signals from multiple sensory modalities work together for kinesthesia. Feedback from cuntaneous receptos, muscle spindles and bvison will be manipulated to determine how the different sources of kinesthetic information are "integrated" to provide our kinesthetic ability. Cutaneous receptors will be activated by stretching the skin to mimic the way that skin stretches during natural movements. Muscle spindles will be activated by exploiting history dependent changes in their discharge (thixotropy), to evoke illusions of altered postion, and vibration will be used to produce illusions of movement. Vision will be manipulated by having participants view their arm in a virtual reality space in which at times the virtual hand accurately reflects their own movements and other times the virtual hand is controlled by the experimenter. The various input signals (cutaneous receptors, muscle spindles, vision, corollary discharge) will be manipulated such that they are either all consistent with a given movement (i.e. flexion or extension) or conflict (i.e. cutaneous and muscle input consistent with flexion, vision and corollary discharge consistent with extension). In some experiments participants will match perceived movements of the (stationary) experimental limb with voluntary movements around the homologous joint on the opposite side of the body. The amplitude of the voluntary "matching'" movements will be used to quantify the amplitude of illusory movements perceived under different conditions. In other experiments, participants will reach or point to virtual targets and the influence of the various input signals will be assessed by errors in trajectories and end points. The results of these experiments will contribute to our understanding of how different sensory modalities are used for kinesthesia.