OTHER QUESTIONS
What kind of electrode configurations can be recommended?
For a detailed description, please see the document Recommended electrode configurations. There are three important aspects for source analysis and source montages:
1) Electrodes should have equal spacing.
2) A row of inferior temporal electrodes on both sides is important to cover the lower head sufficiently, e.g. F11 (F9), A1, P11 (P9). The lower sites (F11, P11) at a 20% distance are preferable to sites at a 10% distance (F9, P9) from the standard row F7, T7, P7 (same applies to other side).
3) Electrodes should be symmetric between both hemispheres with a midline reference or an implicit reference (e.g. F3+F4). A recommended standard with 33 electrodes adds a midline reference Pz, and F11, A1, P11, FC1, FC5, CP1, CP5 and their homologues over the right hemisphere to the 19 electrodes of the 10-20 system (Fpz, Oz not included). For more details see BESA help chapter on Electrodes. When using caps with more electrodes (64 or 128) inferior electrode and equal spacing are similarly important.
How can I verify that electrode locations were imported correctly?
The electrode locations can be inspected in a 3D view using the menu command 'File|Head surface points and sensors|View'. The fiducials (pre-auricular points and nasion) are plotted as purple cubes, the electrodes are plotted as red disks. By clicking on a disk, the electrode label of a particular location, and its coordinates, can be checked. The calculated head radius is also given (default value is 85 mm if no electrodes were digitized).
How do I import digitized electrode locations and head surface points?
Digitized electrode locations can be provided in a surface point file (extension *.sfp) in ASCII format. It is recommended that the first three digitized coordinates are the fiducials (fiduciary points), labeled 'FidT9', 'FidT10', FidNz', followed by electrodes, and possibly additional skin points. A detailed description of the file and how to import it is given in the BESA help files (chapter: Working with Electrodes and Surface Locations).
How do I change or exclude erroneous head surface point locations?
After importing head surface points, they can be inspected using the menu command 'File|Head surface points and sensors|View'. If some points were not digitized correctly, it should be apparent from the 3D view. To exclude these points, the head surface points can be written to an ASCII file by using the command 'File|Head surface points and sensors|Save all files in head coordinates'. The digitized head surface points are written to a file entitled 'xxx.sfp'. They can be edited using a text editor program. Then the data file can be re-opened in BESA, and the edited head surface point file is read automatically. Important note: When using MEG and EEG simultaneously, it is important that the 'xxx.pos' file is also written and read in the same coordinate system as the surface points!
How do I import digitized electrode locations in combined EEG / MEG measurements with the Neuromag system?
The Neuromag system does not store the electrode names with the coordinates. Thus, it is extremely important that you keep track of the digitization protocol, and provide a file which provides the names of fiducials, electrodes, and additional head surface points in the order of digitization (see BESA help: Working with Electrodes and Surface Locations).
How do I import Top Viewer waveforms into a graphics software for further processing?
Top Viewer waveforms can be exported into encapsulated post script files using the command 'File | Print to File' in the Top Viewer window. Printed files can then be imported into a graphics software (e.g. Corel Draw, Adobe Photoshop). In vector-oriented graphics programs, the scalability of the eps format remains available if you select 'Post Script Interpreted' when importing.