INFLUENCE OF HAND DOMINANCE AND STIMULUS ECCENTRICITY ON THE STARTREACT EFFECT

To investigate physiological and methodological variables influencing the StartReact paradigm by comparing responses between dominant (DOM) and non-dominant (NONDOM) hands, and central (CEN) and peripheral (PER) visual cues. In twenty-one healthy adults (mean age = 19 ± 1 years, 17F), we measured reaction time (RT) in response to a visual cue, a visual-auditory cue, and a visual-startling-auditory cue. The visual stimuli were either CEN (0^∘) or PER (15^∘) from the fovea. EMG was recorded bilaterally from the first dorsal interosseous (FDI) and abductor polis brevis (APB) muscles during 108 bilateral, isometric pinch grip contractions. Reaction time was identified as EMG onset from stimulus, and StartReact was calculated as the difference in RT between visual-auditory and visual-startling cues.
Pairwise comparisons between DOM and NONDOM revealed no differences in RT in response to all six CEN and PER cues (all p>0.5). In the APB, the StartReact was larger in NONDOM compared with DOM in CEN (29±24ms vs 23±18ms, p>0.05) and PER (37±27ms vs 32±22ms, p=0.237). In the FDI, the StartReact was not different in NONDOM compared with DOM in CEN (28±19 ms vs 25±19 ms, p=0.515) and PER (28±19ms vs 34±25ms, p=0.865).
Greater influence of brainstem circuits and a weaker CST dominance on thumb-related motor programs, compared to the dominant hand. Meanwhile, the absence of dominance effects in FDI reflects its consistent dependence on corticospinal control for fine motor precision of the fingers in both hands.