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reference:ft_scalpcurrentdensity [2018/08/23 14:43] (current)
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 +=====  FT_SCALPCURRENTDENSITY =====
 +
 +Note that this reference documentation is identical to the help that is displayed in MATLAB when you type "help ft_scalpcurrentdensity"​.
 +
 +<​html><​pre>​
 +  <a href=/​reference/​ft_scalpcurrentdensity><​font color=green>​FT_SCALPCURRENTDENSITY</​font></​a>​ computes an estimate of the SCD using the
 +  second-order derivative (the surface Laplacian) of the EEG potential
 +  distribution
 + 
 +  The relation between the surface Laplacian and the SCD is explained
 +  in more detail on http://​tinyurl.com/​ptovowl.
 + 
 +  Use as
 +    [data] = ft_scalpcurrentdensity(cfg,​ data)
 +  or
 +    [timelock] = ft_scalpcurrentdensity(cfg,​ timelock)
 +  where the input data is obtained from <a href=/​reference/​ft_preprocessing><​font color=green>​FT_PREPROCESSING</​font></​a>​ or from
 +  <a href=/​reference/​ft_timelockanalysis><​font color=green>​FT_TIMELOCKANALYSIS</​font></​a>​. 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 <a href=/​reference/​ft_topoplotER><​font color=green>​FT_TOPOPLOTER</​font></​a>​.
 + 
 +  The configuration should 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'​)
 +    cfg.feedback ​    = string, '​no',​ '​text',​ '​textbar',​ '​gui'​ (default = '​text'​)
 + 
 +  The finite method require the following
 +    cfg.conductivity = conductivity of the skin (default = 0.33 S/m)
 + 
 +  The spline and finite method require the following
 +    cfg.conductivity = conductivity of the skin (default = 0.33 S/m)
 +    cfg.lambda ​      = regularization parameter (default = 1e-05)
 +    cfg.order ​       = order of the splines (default = 4)
 +    cfg.degree ​      = degree of legendre polynomials (default for
 +                        &lt;=32 electrodes ​ = 9,
 +                        &lt;=64 electrodes ​ = 14,
 +                        &​lt;​=128 electrodes = 20,
 +                        else             = 32
 + 
 +  The hjorth method requires the following
 +    cfg.neighbours ​  = neighbourhood structure, see <a href=/​reference/​ft_prepare_neighbours><​font color=green>​FT_PREPARE_NEIGHBOURS</​font></​a>​
 + 
 +  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 you can use
 +    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.
 + 
 +  See also <a href=/​reference/​ft_preprocessing><​font color=green>​FT_PREPROCESSING</​font></​a>,​ <a href=/​reference/​ft_timelockanalysis><​font color=green>​FT_TIMELOCKANALYSIS</​font></​a>,​ FT_FREQNALYSIS,​ <a href=/​reference/​ft_topoplotER><​font color=green>​FT_TOPOPLOTER</​font></​a>​.
 +</​pre></​html>​