Disorders of the somatosensory system

This chapter reviews impairments of grasping and other fine motor tasks following disorders of the somatosensory system. The first part reports findings from transient anesthesia induced experimentally in healthy human subjects. The second part summarizes studies on the effects of lesions to the peripheral sensory system. Findings in patients with sensory deficits following polyneuropathy or carpal tunnel syndrome are differentiated from chronic complete somatosensory deafferentation. The latter group of very rare subjects provides the unique possibility of investigating the function of the motor system deprived of sensory input. The last part summarizes the effects of central lesions due to stroke or cerebral palsy that frequently affect the somatosensory system. The results for various motor tasks including prehensile movements are reported. Specific emphasis is placed on analyses of grip-force control during object manipulation since somatosensory feedback is particularly important for these activities and ample research has been performed during the last few years, enabling comparisons between patient groups.: Introduction: Clarifying the role of sensory information in the control of voluntary movement and force production is one of the most essential questions in sensorimotor research. The most obvious way to investigate this question is to study the effects of damage to the sensory system on movement execution. Indeed, there was controversy about the effects of a complete lack of sensory information at the beginning of the 20th century.