Age-related GABA- and glutamatergic differences in SMA during bimanual coordination

Abstract

The BTT task was scored as a percentage from 0-100% based on the participant's performance in each trial. The score was based on movement accuracy, direction, rotation frequency and speed. The preliminary percentage of the score was calculated based on the total number of target points covered by the participant's movement trajectory along the target line, divided by the total number of target points (see Fig. 1D in (Adab et al., 2020)). To penalize parallel movements to the target line, an additional formula was calculated as previously described in Hehl et al. (2025). Here, the preliminary percentage P was additionally multiplied by the distance factor D, which lead to the final score S (Hehl et al., 2025) í µí± = í µí± • í µí°· The distance factor D was calculated based on the average distance í µí± ̅ to the target line across each data point within one trial which was divided by 8 and subtracted from 1.: í µí°· = 1 − í µí± ̅ 8 In contrast to Hehl et al. (2025), we adjusted the denominator to 8 instead of 5 based on the population's sensitivity of progress in a similar independent dataset. Our sample included both older and younger adults, whereas Hehl et al. (2025) examined only young adults. This adjustment aimed to minimize floor and ceiling effects.