Variation in Reported Human Head Tissue Electrical Conductivity Values

Area of Science:

• Neuroscience
• Biophysics
• Biomedical Engineering

Background:

• Accurate volume conductor models are crucial for electromagnetic source characterization in the human head.
• Existing head tissue electrical conductivity values from literature are inconsistent, hindering model accuracy.

Purpose of the Study:

• To conduct a meta-analysis of human head electrical conductivity values.
• To identify significant variations and influential factors affecting these measurements.
• To provide updated conductivity values for improved volume conductor modeling.

Main Methods:

• A systematic meta-analysis of 56 publications extracted from 3121 identified papers across three databases.
• Conductivity values were categorized by tissue type and recorded with methodology, measurement conditions, and demographics.
• Statistical analysis was performed to identify significant variations and their causes.

Main Results:

• Significant variations in electrical conductivity were found for whole skull, spongiform layer, white matter (WM), and brain-to-skull-conductivity ratio (BSCR).
• Methodology and participant demographics were identified as significant factors influencing conductivity measurements.
• Weighted average conductivity values were determined for various tissues: scalp (0.41 S/m), whole skull (0.02 S/m), three-layer skull (spongiform 0.048 S/m, inner compact 0.007 S/m, outer compact 0.005 S/m), CSF (1.71 S/m), grey matter (0.47 S/m), WM (0.22 S/m), and BSCR (50.4).

Conclusions:

• Human head tissue electrical conductivity exhibits considerable variation, influenced by measurement methods and demographics.
• Volume conductor models should ideally be personalized; however, using weighted averages from this meta-analysis is recommended when personalized models are not feasible.
• Acknowledging and accounting for this variability is essential for accurate electromagnetic source characterization.