Physical intensity of stimuli modulates motor inhibition by affecting response selection processes in right inferior frontal regions.

Response inhibition is a central aspect of cognitive control. Yet, only recently the role of sensory mechanisms for response inhibition has been addressed and neurophysiological mechanisms are far from being understood. Here we ask in how far the physical intensity of stimuli is a relevant perceptual factor modulating motor inhibitory control. We investigated how different physical (objective) stimulus and the subjectively perceived stimulus magnitude modulated response inhibition and its neurophysiological correlates. To this end we used a somatosensory GO/NOGO task in combination with EEG recordings and applied temporal signal decomposition and source localization methods. The behavioral (false alarm) data clearly demonstrated that response inhibition performance was worse in the subjective and objective stimulation condition as compared to the reference stimulation condition with higher stimulus magnitude. Despite primary perceptual aspects were manipulated, neurophysiological correlates of lower-level perceptual and attentional selection processes did not explain effects on overt response inhibition behavior. Rather, neurophysiological processes at the response selection level were modulated. These were associated with activation differences in the right inferior frontal gyrus and suggest that "braking processes" enabling the inhibition of a to-be-executed motor response were modulated. The modulation of these braking processes depends on objective physical magnitude of incoming sensory information and not the subjectively perceived stimulus magnitude.