Neural correlates of tactile temporal-order judgment in humans: an fMRI study.

Little is known about the neuronal mechanisms underlying the temporal ordering of tactile signals. We examined the brain regions involved in judgments of the temporal order of successive taps delivered to both hands. Participants received identical stimuli while engaging in 2 different tasks: Judging the temporal order and judging the numerosity of points of tactile stimulation. Comparisons of the functional magnetic resonance imaging data obtained during the 2 tasks revealed regions that were more strongly activated with the judgments of the temporal order than with the judgments of numerosity under both arms-uncrossed and -crossed conditions: The bilateral premotor cortices, the bilateral middle frontal gyri, the bilateral inferior parietal cortices and supramarginal gyri, and the bilateral posterior part of the superior and middle temporal gyri. Stronger activation was found in some of these areas that implicated for remapping tactile stimuli to spatial coordinates after the participants crossed their arms. The activation in the perisylvian areas overlapped with the human visual-motion-sensitive areas in the posterior part. Based on these results, we propose that the temporal order of tactile signals is determined by combining spatial representations of stimuli in the parietal and prefrontal cortices with representations of "motion" or "changes" in the multisensory perisylvian cortex.