Neural correlates underlying motor sequence task performance: handedness and sequence complexity

Purpose We aimed to determine the neural correlates of motor sequence performance in healthy young adults, with respect to handedness and sequence complexity. Methods Strongly left-handed (LH, n = 15, 24.9y) and right-handed (RH, n = 15, 26.4y) participants performed finger key presses on a numeric keypad at four levels of sequence complexity with each hand in a randomized order. Results Both LH and RH performed the motor sequence task with faster reaction and motor execution times when using their right hand, irrespective of sequence complexity. Increasing motor-sequence complexity reduced frontal and parietal EEG power in both LH and RH, particularly at the highest complexity level, while RH also showed increased occipital delta activity when using the non-dominant hand, indicating that both sequence complexity and handedness modulate cortical activity during motor sequence performance. In addition, connectivity analysis showed significant hemispheric differences in brain network organization across frequency bands, with mainly greater left-hemisphere frontal and occipital connectivity but stronger right-hemisphere parietal connectivity. Sequence complexity primarily influenced functional connectivity (wPLI) rather than network topology. Notably, connectivity measures and selected MST-derived graph-theoretical metrics were linked to motor performance. Conclusion Our findings suggest that motor-sequence performance is faster with the right hand, regardless of handedness and sequence complexity, which relies on a consistently organized hemispheric network, while increasing task complexity is managed primarily through frequency-specific changes in functional connectivity rather than large-scale reorganization of network structure.