NIRS-EEG joint imaging during transcranial direct current stimulation: Online parameter estimation with an...

Area of Science:

• Neuroscience
• Biomedical Engineering
• Signal Processing

Background:

• Transcranial direct current stimulation (tDCS) influences brain activity and blood flow, but its mechanisms remain unclear.
• Monitoring tDCS effects requires understanding the interplay between neural activity and hemodynamics.
• Electroencephalography (EEG) and near-infrared spectroscopy (NIRS) are key tools for such monitoring.

Purpose of the Study:

• To develop and validate an online method for tracking the coupling between EEG and NIRS signals during tDCS.
• To investigate the transient changes in brain activation during tDCS using a novel signal processing approach.
• To overcome limitations of conventional methods in analyzing time-varying physiological signals.

Main Methods:

• Utilized a Kalman Filter to estimate parameters of an autoregressive (ARX) model for online analysis.
• Applied the method to track the coupling between EEG power spectrum and NIRS oxy-hemoglobin signals during anodal tDCS.
• Employed a 4x1 ring high-definition montage for tDCS application in 5 healthy subjects.

Main Results:

• The online ARX parameter estimation successfully detected transient changes in EEG-NIRS coupling during resting-state brain activation.
• The method demonstrated sensitivity in capturing dynamic relationships between electrophysiological and hemodynamic signals.
• This approach overcomes the subjectivity and time-invariance issues inherent in sliding window cross-correlation.

Conclusions:

• A novel online ARX model-based tracking method enables continuous assessment of EEG-NIRS coupling during tDCS.
• This technique provides a valuable tool for understanding resting-state brain activation under neuromodulation.
• The findings contribute to a deeper understanding of tDCS-induced neurophysiological and hemodynamic changes.