Current-source density (CSD) transformation / Surface Laplacian

Convert EEG data to reference-free current-source density (CSD) transformed data (i.e., surface Laplacian).

Requirements

• MATLAB installed
• EEGLAB installed
• Some EEG data

Usage

1. Load EEG data into EEGLAB

2. load channel locations

3. type in command window:

EEG = csd_transform(EEG);

Comparison with conventional referencing methods

Here is a comparison of ERP between emotional and neutral stimuli for each method to assess how the referencing method affects statistical results at the group level (N = 81; p<0.01 after spatiotemporal cluster-correction). This illustrates well how CSD-transformation increases spatial resolution and helps highlight local dynamics, whereas AV- and REST- referenced data increase global dynamics.

Reference to Average (left), Infinity (middle), and Surface Laplacian transformation (right)

Literature

Nunez, P. L., Silberstein, R. B., Cadusch, P. J., Wijesinghe, R. S., Westdorp, A. F., & Srinivasan, R. (1994). A theoretical and experimental study of high resolution EEG based on surface Laplacians and cortical imaging. Electroencephalography and clinical neurophysiology, 90(1), 40-57.

https://www.sciencedirect.com/science/article/abs/pii/0013469494901120

Tandonnet, C., Burle, B., Hasbroucq, T., & Vidal, F. (2005). Spatial enhancement of EEG traces by surface Laplacian estimation: comparison between local and global methods. Clinical neurophysiology, 116(1), 18-24.

https://www.sciencedirect.com/science/article/abs/pii/S1388245704002676

Carvalhaes, C., & De Barros, J. A. (2015). The surface Laplacian technique in EEG: Theory and methods. International Journal of Psychophysiology, 97(3), 174-188.

https://www.sciencedirect.com/science/article/abs/pii/S0167876015001749

Kayser, J., & Tenke, C. E. (2015). Issues and considerations for using the scalp surface Laplacian in EEG/ERP research: A tutorial review. International Journal of Psychophysiology, 97(3), 189-209.

https://www.sciencedirect.com/science/article/abs/pii/S0167876015001609

Kayser, J., & Tenke, C. E. (2015). On the benefits of using surface Laplacian (current source density) methodology in electrophysiology. International journal of psychophysiology: official journal of the International Organization of Psychophysiology, 97(3), 171.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4610715/