Thumb-pointing in humans after damage to somatic sensory cortex

Three patients with a severe somatosensory deficit consequent on damage of the right somatosensory cortices were required, while blindfolded, to point with their insensate thumb to select positions on the other left fingers. Given the absence of feedback, the motor performance of the insensate thumb appeared grossly impaired in all patients. However, all patients attained end-points with an accuracy greater than chance. This result suggests that spatial accuracy may not rely entirely on sensory feedback. A good accuracy of pointing was evinced also in potentially facilitating conditions where somatosensory and motor cues coming from the intact side during simultaneous movement of both thumbs, vision of stimulated point and final thumb position, and visuomotor imagery were available. Furthermore, in one patient, the accuracy of the insensate thumb in cued conditions was higher than in a reference baseline condition, thus indicating that motor and cognitive cues can help the motor performance of patients with cortical somatosensory lesions.