Effect of kinesthetic force feedback and visual sensory input on writer´s cramp

Writer´s cramp, a task specific dystonia is felt to be a disorder of sensorimotor integration involving the basal ganglia and cortex. Motivated by this fact, in the present study we investigated the effects of haptic and visual sensory inputs on cramp severity and frequency during a trial. For this goal seven subjects with writer´s cramp disease were asked to perform the trial, which included writing, hovering, and spiral/sinusoidal drawing subtasks. The trial had three major steps namely: A) normal writing, when the patients write without sensory manipulation, B) robotics-assisted writing, when a haptic device supports the pen and provides a compliant writing surface with the goal of manipulating the kinesthetic haptic input, and C) blindfolded writing, when the patients were asked to write while being blindfolded, with the goal of analyzing the potential effects of vision feedback in sensorimotor integration pathway. The number of cramps that occurred and subjective measures of patient feedback about cramp severity were analyzed. The results show that reducing the writing surface rigidity, and blocking vision feedback while writing, changes the cramp pattern and decreases the overall cramp severity.