Data processing was completed using the open-source software HOMER2 (53), which is implemented in MATLAB (MathWorks). First, channels with signal quality outside of the range of 80 to 140 dB were excluded. The remaining raw optical signals (intensity at 690 and 830 nm) were converted into optical density using the modified Beer-Lambert law with a partial path-length factor of 6.4 (690 nm) and 5.8 (830 nm) (5456). Motion artifacts and systemic physiology interference were corrected using recursive principal component analysis and low-pass filters (53, 57, 58). The filtered optical density data were used to derive the delta concentrations of oxyhemoglobin and deoxyhemoglobin.

The short-distance channels were regressed from the long-distance channels to remove any interference originating from superficial layers. This was achieved by using a consecutive sequence of Gaussian basis functions via ordinary least squares to regress scalp and dura activation data collected from the short separation fibers to create the hemodynamic response function (HRF) (17, 18, 59). The corresponding source and detector pairs for each source were averaged over the task start and end time for each trial and subject (as shown in fig. S1). For example, if a subject performed five trials, then the HRF would be group-averaged over the task stimulus for each trial, ensuring that rest periods were not included in the group average. It is important to note that the task stimulus period for a given trial of each subject may vary because of motor skill proficiency, as seen in varying task completion times (table S3). The result is a scalar value for the change in oxyhemoglobin according to different brain regions for all participants. Finally, scalar values for each of the 32 channels were grouped into eight distinct regions of interest according to the anatomical structures as follows: left PFC (source 1, detectors 1 and 2), medial PFC (source 2, detectors 2 and 3), right PFC (source 3, detectors 3 and 4), left lateral M1 (source 4, detectors 5 to 8), LMM1 (source 5, detectors 8 to 10), right medial M1 (source 6, detectors 9 to 12), right lateral M1 (source 7, detectors 11 to 14), and finally, SMA (source 8, detectors 9, 15, and 16).

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