Modulation of somatosensory processing in dual tasks: an event-related brain potential study.

The amplitudes of the event-related brain potentials (ERPs) have been associated with the amount of attentional resources. The present study investigated whether force production type (increasing or decreasing force) in a visuomotor force tracking task modulates the ERPs elicited in a somatosensory oddball task performed simultaneously, whether stimulus-response coupling assessed by a single-trial analysis of P300 latency is modulated by the concurrent performance of the tasks, and whether dynamic visuomotor coordination rather static coordination is sensitive to the ERP modulation. In the dual-task condition, the subjects tracked a target line moving on the display with another line representing the force generated by the grip of their left hand, while executing the somatosensory oddball task with the right hand. In the oddball-only condition, the oddball task only was performed. The amplitude of the P300 elicited in the oddball task was decreased in the dual-task condition compared with the oddball-only condition, and further decreased in the force-decreasing phase compared with the increasing phase, but was not altered by the concurrently performed isometric contraction. P100, N140, reaction time (RT), and error rate were not influenced by force production type. A correlation analysis of single-trial P300 latency and RT showed that the dual-task condition produced a stronger coupling of the P300 and RT. In summary, different force production types requiring dynamic visuomotor coordination alter a modality-nonspecific late stage of somatosensory processing but have less of an effect on early stages. During the performance of the dual task, stimulus-response coupling in the somatosensory discrimination task becomes stronger to compensate for a lack of resources and/or due to snap decisions owing to sufficient resources.