Task requirements change signal strength of the primary somatosensory M50: Oddball vs. one-back tasks.

Studies on attention to tactile stimuli have produced conflicting results concerning the possibility and/or direction of modulation of early somatosensory-evoked fields (SEFs). To evaluate sources of these conflicting results, the same subjects performed four different tasks in which the stimulation site, type, and intensity were kept constant. Twelve subjects performed an oddball-like tactile task, two different one-back tactile tasks, and a visual task, while two distal phalanges of the index and ring finger were stimulated. Task-dependent SEF modulations were found as early as 50 ms after stimulus onset (M50 component). Target/non-target ratios of M50 revealed enhanced values for the oddball-like tactile task, but decreased values for the tactile one-back task. This indicates that previously obtained conflicting results might be due to different central mechanisms induced by different task requirements.