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Trunk rotation and handedness modulate cortical activation in neglect-associated regions during temporal order judgments.

ABSTRACT: The rotation of the trunk around its vertical midline could be shown to bias visuospatial temporal judgments towards targets in the hemifield ipsilateral to the trunk orientation and to improve visuospatial performance in patients with visual neglect. However, the underlying brain mechanisms are not well understood. Therefore, the goal of the present study was to investigate the neural effects associated with egocentric midplane shifts under consideration of individual handedness. We employed a visuospatial temporal order judgment (TOJ) task in healthy right- and left-handed subjects while their trunk rotation was varied. Participants responded by a saccade towards the stimulus perceived first out of two stimuli presented with different stimulus onset asynchronies (SOA). Apart from gaze behavior, BOLD-fMRI responses were measured using functional magnetic resonance imaging (fMRI). Based on findings from spatial neglect research, analyses of fMRI-BOLD responses were focused on a bilateral fronto-temporo-parietal network comprising Brodmann areas 22, 39, 40, and 44, as well as the basal ganglia core nuclei (caudate, putamen, pallidum). We observed an acceleration of saccadic speed towards stimuli ipsilateral to the trunk orientation modulated by individual handedness. Left-handed participants showed the strongest behavioral and neural effects, suggesting greater susceptibility to manipulations of trunk orientation. With respect to the dominant hand, a rotation around the vertical trunk midline modulated the activation of an ipsilateral network comprising fronto-temporo-parietal regions and the putamen with the strongest effects for saccades towards the hemifield opposite to the dominant hand. Within the investigated network, the temporo-parietal junction (TPJ) appears to serve as a region integrating sensory, motor, and trunk position information. Our results are discussed in the context of gain modulatory and laterality effects.

SUBMITTER: Paschke K

PROVIDER: S-EPMC6627032 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:A considerable body of sensory research has addressed the rules governing simultaneity judgments (SJs) and temporal order judgments (TOJs). In principle, neural events that register stimulus-arrival-time differences at an early sensory stage could set the limit on SJs and TOJs alike. Alternatively, distinct limits on SJs and TOJs could arise from task-specific neural events occurring after the stimulus-driven stage. To distinguish between these possibilities, we developed a novel reaction-time (RT) measure and tested it in a perceptual-learning procedure. The stimuli comprised dual-stream Rapid Serial Visual Presentation (RSVP) displays. Participants judged either the simultaneity or temporal order of red-letter and black-number targets presented in opposite lateral hemifield streams of black-letter distractors. Despite identical visual stimulation across-tasks, the SJ and TOJ tasks generated distinct RT patterns. SJs exhibited significantly faster RTs to synchronized targets than to subtly asynchronized targets; TOJs exhibited the opposite RT pattern. These task-specific RT patterns cannot be attributed to the early, stimulus-driven stage and instead match what one would predict if the limits on SJs and TOJs arose from task-specific decision spaces. That is, synchronized targets generate strong evidence for simultaneity, which hastens SJ RTs. By contrast, synchronized targets provide no information about temporal order, which slows TOJ RTs. Subtly asynchronizing the targets reverses this information pattern, and the corresponding RT patterns. In addition to investigating RT patterns, we also investigated training-transfer between the tasks. Training to improve SJ precision failed to improve TOJ precision, and vice versa, despite identical visual stimulation across tasks. This, too, argues against early, stimulus-driven limits on SJs and TOJs. Taken together, the present study offers novel evidence that distinct rules set the limits on SJs and TOJs.

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Trunk rotation and handedness modulate cortical activation in neglect-associated regions during temporal order judgments.

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