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Construct EEG Forward Model (Leadfield Matrix)

Source: R/eeg-source.R
eegForwardModel.Rd

Constructs a leadfield matrix that maps brain source activity to scalp electrode potentials. Uses electrode positions from colData(x) if available, otherwise falls back to standard 10-20 system positions on a unit sphere.

Usage

eegForwardModel(
  x,
  method = c("spherical", "bem_simplified", "bem", "sphere_analytic", "nyhead",
    "fsaverage"),
  n_sources = 500,
  assay_name = NULL
)

Arguments

x

A PhysioExperiment object with EEG data.

method

Forward model method: "spherical" (current dipole in infinite homogeneous medium with conductivity 0.33 S/m), "bem_simplified" (3-shell Berg and Scherg 1994 approximation), "sphere_analytic" (the analytic single-sphere leadfield over a structured spherical cortical source space), "bem" (a 3-shell boundary element method over the same source space), or "nyhead" / "fsaverage" (published head models loaded on demand). The last four require the PhysioHeadModels package; the "nyhead" / "fsaverage" methods additionally require the corresponding dataset to have been downloaded (see PhysioHeadModels::fetchNYHead).

n_sources

Number of dipole sources to distribute inside the head model (default: 500).

assay_name

Name of the assay to reference for channel count. If NULL, the default assay is used.

Value

A list with components:

leadfield

Numeric matrix of dimensions n_electrodes x (n_sources * 3). Each source has 3 orientation columns (x, y, z).

source_positions

Data frame with columns x, y, z for each source location.

electrode_positions

Data frame with columns label, x, y, z for each electrode.

n_sources

Integer number of source dipoles.

source_normals

For the realistic methods, an n_sources x 3 matrix of cortical surface normals (absent for the legacy methods).

method

The resolved forward-model method.

coordinate_provenance

Source-space origin, units, and anatomical fidelity used by coordinate-aware plotting functions.

References

Pascual-Marqui, R. D. (2002). Standardized low-resolution brain electromagnetic tomography (sLORETA). Methods and Findings in Experimental and Clinical Pharmacology, 24(Suppl D), 5-12.

See also

eegSourceEstimate(), eegBeamformer(), eegSourcePower()

Examples

if (FALSE) { # \dontrun{
pe <- make_eeg(n_time = 1000, n_channels = 19, sr = 250)
fm <- eegForwardModel(pe, method = "spherical", n_sources = 100)
dim(fm$leadfield)
} # }