FieldTrip

Note that this reference documentation is identical to the help that is displayed in Matlab when you type “help ft_scalpcurrentdensity”.

  FT_SCALPCURRENTDENSITY computes an estimate of the SCD using the
  second-order derivative (the surface Laplacian) of the EEG potential
  distribution
 
  Use as
    [data] = ft_scalpcurrentdensity(cfg, data)
  or
    [timelock] = ft_scalpcurrentdensity(cfg, timelock)
  where the input data is obtained from FT_PREPROCESSING or from
  FT_TIMELOCKANALYSIS. The output data has the same format as the input
  and can be used in combination with most other FieldTrip functions
  such as FT_FREQNALYSIS or FT_TOPOPLOTER.
 
  The configuration can contain
    cfg.method       = 'finite' for finite-difference method or
                       'spline' for spherical spline method
                       'hjorth' for Hjorth approximation method
    cfg.elecfile     = string, file containing the electrode definition
    cfg.elec         = structure with electrode definition
    cfg.trials       = 'all' or a selection given as a 1xN vector (default = 'all')
 
  The spline and finite method require the following
    cfg.conductivity = conductivity of the skin (default = 0.33 S/m)
  
  The hjorth method requires the following
    cfg.neighbours   = neighbourhood structure, see FT_PREPARE_NEIGHBOURS
 
  Note that the skin conductivity, electrode dimensions and the potential
  all have to be expressed in the same SI units, otherwise the units of
  the SCD values are not scaled correctly. The spatial distribution still
  will be correct.
 
  To facilitate data-handling and distributed computing with the peer-to-peer
  module, this function has the following options:
    cfg.inputfile   =  ...
    cfg.outputfile  =  ...
  If you specify one of these (or both) the input data will be read from a *.mat
  file on disk and/or the output data will be written to a *.mat file. These mat
  files should contain only a single variable, corresponding with the
  input/output structure.
 
  The 'finite' method implements
    TF Oostendorp, A van Oosterom; The surface Laplacian of the potential:
    theory and application. IEEE Trans Biomed Eng, 43(4): 394-405, 1996.
    G Huiskamp; Difference formulas for the surface Laplacian on a
    triangulated sphere. Journal of Computational Physics, 2(95): 477-496,
    1991.
 
  The 'spline' method implements
    F. Perrin, J. Pernier, O. Bertrand, and J. F. Echallier.
    Spherical splines for scalp potential and curernt density mapping.
    Electroencephalogr Clin Neurophysiol, 72:184-187, 1989
  including their corrections in
    F. Perrin, J. Pernier, O. Bertrand, and J. F. Echallier.
    Corrigenda: EEG 02274, Electroencephalography and Clinical
    Neurophysiology 76:565.
 
  The 'hjorth' method implements
    B. Hjort; An on-line transformation of EEG scalp potentials into
    orthogonal source derivation. Electroencephalography and Clinical
    Neurophysiology 39:526-530, 1975.