Trial-to-trial variability differentiates motor imagery during observation between low versus high responders: a functional near-infrared spectroscopy study.
Trial-to-trial variability is a well-known issue in brain signals measured using functional near-infrared spectroscopy (fNIRS). We aimed to investigate whether trial-to-trial variability does provide information about individual performance. Seventeen subjects observed a virtual reality grasping task in first-person view while either imagining (motor imagery during observation, MIO) or imitating (motor execution, ME) the movements. Each condition was performed with the display in one of two positions, a conventional vertical position and a mirrored horizontal position which placed the virtual arm in the correct position relative to the viewpoint. Averaged oxy-hemoglobin concentration Δ[O(2)Hb] showed that the responses could be differentiated into two distinct groups: low responders (LR) and high responders (HR). Within groups, two main sources of trial-to-trial variability were identified: (a) the Δ[O(2)Hb] amplitude, with largest amplitudes in ME conditions (group HR) and smallest amplitudes in MIO conditions (group LR), and (b) the sign of Δ[O(2)Hb], with positive responses occurring most frequently during ME (group HR) and negative responses most frequently during MIO (group LR). Furthermore, the trial-to-trial dynamics differed between groups and could be described in group LR as inverted polynomial U-shaped curve in the mirror conditions (ME-mirror, MIO-mirror). Last, trial-to-trial variability was significantly dependent on task modality, i.e. ME (group HR) versus MIO (group LR), and/or the mirrored display positions (group LR). Our results show a relationship of trial-to-trial variability to individual MI performance, which may be of significance for neurorehabilitation applications. Although the sources of trial-to-trial variability remain unknown, we suggest that they may contribute to future neurofeedback applications.
Biomedical Optics Research Laboratory, Division of Neonatology, University Hospital Zurich, Frauenklinikstrasse 10, 8091 Zurich, Switzerland. holper@ini.phys.ethz.ch
Lisa
L
Holper
Nagisa
N
Kobashi
Daniel
D
Kiper
Felix
F
Scholkmann
Martin
M
Wolf
Kynan
K
Eng
D000328:Adult; D000704:Analysis of Variance; D001931:Brain Mapping; D016002:Discriminant Analysis; D004576:Electromyography; D005260:Female; D007839:Functional Laterality; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D019018:Imagery, Psychotherapy; D008297:Male; D009044:Motor Cortex / Q000378:metabolism*; D009068:Movement / Q000502:physiology*; D019370:Observation; D010108:Oxyhemoglobins / Q000378:metabolism*; D019265:Spectroscopy, Near-Infrared; D055815:Young Adult
D006454:Hemoglobins; D010108:Oxyhemoglobins; C100003:deoxyhemoglobin