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

  FT_HEADMODEL_CONCENTRICSPHERES creates a volume conduction model
  of the head based on three or four concentric spheres. For a 3-sphere
  model the spheres represent the skin surface, the outside of the
  skull and the inside of the skull For a 4-sphere model, the surfaces
  describe the skin, the outside-skull, the inside-skull and the inside of the
  cerebro-spinal fluid (CSF) boundaries.
  The innermost surface is sometimes also referred to as the brain
  surface, i.e. as the outside of the brain volume.
  This function takes as input a single headshape described with
  points and fits the spheres to this surface. If you have a set of
  points describing each surface, then this function fits the spheres
  to all individual surfaces.
  Use as
    headmodel = ft_headmodel_concentricspheres(mesh, ...)
  Optional input arguments should be specified in key-value pairs and can
    conductivity = vector with the conductivity of each compartment
    fitind       = vector with indices of the surfaces to use in fitting the center of the spheres