fNIRS dataset for the analysis of oxygen saturation in the primary motor cortex during a single hand movement.

Sixteen healthy volunteers (age: 20-45 years, males) participated in the experiment. All the participants were right-handed, amateur practitioners of physical exercises, and non-smokers. The subjects were conditionally healthy: no diagnosed diseases of the musculoskeletal or nervous system, no prescribed medications. Prior to the experiment, the participants were asked to maintain a healthy lifestyle for a least 48 hours, including 8-hours night rest, prohibited alcohol consumption, limited caffeine consumption, and moderate physical activity.The experiments were held in the first half of the day in a room with a sufficient natural lighting level. Before the beginning of the experiment, the volunteers were instructed about its goals and methods, along with possible inconveniences. The participants were able to ask any related questions and receive detailed answers. After all explanations, each participant filled and signed the blank of informed written consent before participating in the experiment. The experimental procedure was performed following the Helsinki’s Declaration and approved by the local Ethics Committee of the Innopolis University.The fNIRS signals were recorded with the “NIRScout” device by “NIRx” (Germany). The NIRScout system uses 8 sources and 8 detectors to record hemodynamic response in the cortex with a sampling rate of 7.8125 Hz. Optodes are placed non-invasively on the subject’s scalp by mounting to the sockets of the special cap by “EASYCAP” (Germany). FNIRS channels were formed by “source-detector” pairs that were placed close enough to each other. The optimal distance between source and detector is about 3 cm due to the specific traveling path of near-infrared light in cortex’s tissue: the light diffuses in the tissue and at a depth of approximately 3 cm is reflected towards the detector, forming a so-called “banana-shaped” path.In our experiments, we placed optodes in the primary motor cortex area (M1), as shown in Fig. 1. Fig. 1 illustrates our montage with overall 23 fNIRS channels. Additionally, 8 EEG electrodes located according to the international scheme “10-10” are shown as the reference for a better understanding of optodes’ placements.EMG signals were recorded with POLY channels of the encephalograph “Encephalan-EEGR-19/26” by “Medicom- MTD” (Russia). In our study, we used special EMG sensors with two recording electrodes and one ground electrode. Such a scheme allows recording the envelope of EMG signal with a sampling rate of 250 Hz. EMG envelope is related to muscular contractions, and in our experiment, it was used to assess hand movements while high-frequency EMG component was filtered (with a low-pass filter with cutoff frequency – 1 Hz). EMG electrodes were placed non-invasively on the forearm muscle on each of the subject’s hands. Before electrode mounting, the skin was treated with abrasive gel “NuPrep” to ensure good conductivity and high quality of recorded EMG signals. As recording electrodes, we used disposable, pre-gelled adhesive electrodes “Sticktrode” by “Neuroelectrics” (Spain).All experimental work was carried out in the Neuroscience and Cognitive Technology Laboratory of the Innopolis University.The experiment was performed as follows. The subject was sitting in a comfortable chair with hands placed on armrests. The monitor was placed in front of the subject’s eyes at a distance of 70-80 cm for demonstration of visual commands. Each experiment began and ended with a 3-min recording of background brain activity, during which the subject was instructed to relax and make no hand movements. During the active phase of the experiment, the subject was asked to perform movements with his/her left or right hand according to the screen instructions. There were 40 total hand movement trials (20 for each hand) that were performed in random order.<br><br>Each hand movement trial consisted of several phases accompanied by specific commands on the monitor. The trial started with the fixation of the subject’s attention — a bright cross appeared on a black screen for 2 seconds and acted as a signal for the subject to prepare for the trial. Attention fixation was followed by a visual cue: the cross stayed on the screen, and the left- or right-oriented arrow appeared on the top of it for 1.5 seconds. During this phase, the subject was informed that the left- or right-hand movement (correspondingly) was required. The next phase was motor execution: the arrow disappeared from the screen, but the cross stayed for 5 seconds. During this time interval, the subject performed the required hand movement. Hand movement consisted of bending and unbending of fingers to the palm’s center, similar to clenching of the imaginary ball. The trial ended with rest: the cross disappeared, and the black screen was shown for 15 seconds. During this phase, the subject rested and waited for the next command.We applied a band-pass filter (0.01 − 0.1 Hz) to pre-process experimental fNIRS data before all calculations based on the modified Beer-Lambert law. FNIRS data acquisition and pre-processing procedures were performed with “NIRScout” software.For each subject, EMG and fNIRS trials were time-locked to the command and averaged across all trials corresponding to the left and right-hand movements. Thus, event-related EMG/fNIRS signals were obtained. On the group level, the 7-s EMG trials were tested against the baseline separately for the left and right hands. The 18-s fNIRS trials were corrected to the baseline as (SaO2 − SaO2base)/SaO2base and contrasted between the left-hand and right-hand movements.