def _voxel_brain(data, lut, vmin, vmax):
    """Plot spheres for volume source space

    Parameters
    ----------
    data : NDVar
        Data to plot.
    lut : array
        Color LUT.
    vmin, vmax : scalar
        Data range.
    """
    if data.dimnames != ('source',):
        raise ValueError('Can only plot 1 dimensional source space NDVars')
    from mayavi import mlab
    x, y, z = data.source.coordinates.T
    figure = mlab.figure()
    mlab.points3d(x, y, z, scale_factor=0.002, opacity=0.5)
    pts = mlab.points3d(x, y, z, data.x, vmin=vmin, vmax=vmax)
    pts.module_manager.scalar_lut_manager.lut.table = lut
    return figure
