# Getting started with LORETA

LORETA-KEY is a software program implemented by Roberto Pascual-Marqui that implements the LORETA source localization algorithm (“low resolution brain electromagnetic tomography”). The software is available from the LORETA home page. Using LORETA-KEY, you can make a distributed source reconstruction for EEG data, using a three-shell spherical head model registered to a standardized stereotactic space (based on MNI brain). The source reconstruction is restricted to cortical gray matter.

The LORETA2FIELDTRIP function can be used to read in the resulting files (*.slor, *.lorb) from the LORETA-KEY software. The output of the LORETA2FIELDTRIP function is a matlab structure that is equivalent to the structures that result from the **ft_sourceanalysis** function in FieldTrip. Hence, you can use its output as input in the FieldTrip **ft_sourcegrandaverage** and/or **ft_sourcestatistics** functions.

Using sourcestatistics, you can perform a random-effect parametric or non-parametric statistical test based on a single-voxel statistic or based on a spatio-temporal cluster statistic (only non-parametric). Both the parametric and non-parametric statistical tests implemented in FieldTrip have support for correcting for the multiple comparison problem.

## STEPS

To use sLORETA data in FieldTrip, you need to do the following steps.

### Convert the sLORETA source to a text file

- In the LORETA program, you go to main utilities > Format converter.
- There you select: input binary file (sLORETA)
- It does not matter which format for output you choose, the code will figure it out. In the text file, rows are the time points, columns are the volume-gridpoints (called voxels).
- After using loreta2fieldtrip the data is in FieldTrip volume format in MNI space.

### Hints on plotting the LORETA source

For use in **ft_sourceplot** with method *“slice”* or *“ortho”* you can use the MNI template as anatomy

% Read in the MNI template from SPM: template = ft_read_mri([cur_path_FT, '\external\spm8\templates\T1.nii']); % Interpolate your LORETA volume on the MNI template: [interp_mean] = ft_sourceinterpolate(cfg, GA_mean, template);

For method *“surface”* you don't need to interpolate. However, you have to use a large sphereradius (15 for instance) to pull the source to plot nicely on the surface.

Also see the plotting tutorial.