Author(s): NÉGYESI, J., ZHAO, J., WANG, Y., BOLLA, G., BECSKE, M., HORVÁTH, A.A., KOVÁCS, P.M., SHIOIRI, S., NAGATOMI, R., Institution: HUNGARIAN UNIVERSITY OF SPORTS SCIENCE, Country: HUNGARY, Abstract-ID: 214

INTRODUCTION:
Reaction and motor task performance times vary depending on whether the dominant or non-dominant hand is involved in practice, reflecting the brain's functional lateralization. A large body of research indicates that this laterality is related to the complexity of the motor task sequence. In contrast, our previous study indicates that handedness did not affect motor skill acquisition with the dominant hand or interlimb transfer to the non-dominant hand, regardless of task complexity. In the present study, we aimed to determine the electroencephalography (EEG)-derived neural correlates of this phenomenon.
METHODS:
In this study, strongly left-handed (n = 15, mean age = 24.9 y) and right-handed (n = 15, 26.4 y) participants performed finger key presses on a numeric keypad across four levels of sequence complexity, with hand order randomized. Furthermore, they performed motor sequence practice with the dominant hand to assess its effects on accuracy, reaction time, and movement time immediately (POST) and 24 hours (24H) after practice. EEG data were also recorded to investigate spontaneous brain electrical activity during the motor sequence tasks.
RESULTS:
Participants responded and performed the motor sequence task faster at each level of complexity over time (all p < 0.05). This was associated with an immediate increase in mean 𝛼 power, which returned to baseline levels 24H after practice in each brain area (all p < 0.05). The mean 𝛽 power of each brain area decreased after practice and decreased further 24 hours after practice in the parietal (p = 0.032, d = 0.200) and temporal (p = 0.042, d = 0.209) areas. Surprisingly, mean 𝜃 power differed only between POST and 24H over the parietal cortex (p = 0.036, d = 0.230). In addition, there were also sequence complexity × hand × handedness interaction effects in both RT (F2.2, 61.9 = 15.355, p < 0.001, 𝜂p2 = 0.354) and MT (F2, 55.3 = 16.477, p < 0.001, 𝜂p2 = 0.370). Post-hoc results clarified that the faster RT and MT in the right vs. left hand was present at level 3 in left-handed participants (RT: p = 0.003, d = 0.594, MT: p = 0.010, d = 0.379) and for level 3 (RT: p = 0.003, d = 0.609, MT: p < 0.001, d = 0.533) and level 4 (RT: p = 0.031, d = 0.599, MT: p = 0.007, d = 0.603) in right-handers. Nevertheless, these were not associated with changes in any EEG power band.
CONCLUSION:
Although the behavioural data from the present study are consistent with our previous results, changes in EEG power bands appear to account for only part of the underlying mechanisms. We are examining whether alterations in brain connectivity influence how handedness interacts with the complexity of motor sequence tasks after dominant-hand practice. However, recent studies over the past decade suggest that epigenetic regulation within the spinal cord is foundational for handedness. Consequently, the spinal cord might also significantly contribute to determining handedness.