Active Movement Reduces the Tactile Discrimination Performance

Self-performed arm movements are known to increase the tactile detection threshold (i.e., decrease of tactile sensitivity) which is part of a phenomenon called tactile suppression. Today, the origin and the effects of tactile suppression are not fully understood. Tactile discrimination tasks have been utilized to quantify the changes in tactile sensitivity due to arm movements and to identify the origin of tactile suppression. The results show that active arm movement also increases tactile discrimination thresholds which has never been shown before. Furthermore, it is shown that tactile sensitivity drops at approximately 100 ms before the actual arm movement. We conclude that tactile suppression has two origins: (1) a movement related motor command which is a neuronal signal that can be measured 100 ms before a muscle contraction. This motor command is the origin for the increase of the discrimination threshold prior to the arm movement and (2) task irrelevant sensory input which reduces tactile sensitivity after the onset of the arm movement.