Tags: template eeg meg opm layout

Template 2-D layouts for plotting

EEG electrode and MEG gradiometer positions in the layouts are represented as points in 2-D Cartesian space, i.e. with an X and Y position for each electrode. Furthermore, each electrode has a label. In the layout tutorial you can find more details on how to create and use them. The file format for layout files specified as ASCII .lay files is explained here.

EEG layouts

Standard 10-20, 10-10 and 10-5 caps

The following template layouts are for an electrode cap based on a standard 10-20 (20%), 10-10 (10%) and 10-5 (5%) montage.

BrainProducts

The following template layouts are for electrode caps from Brain Products. FieldTrip provides .mat files (since r6121 - june 2012) that are based on the bitmap images shown below. Note that some of these layouts were created specifically for the DCCN, DCC and MPI, and may differ from other actiCAP layouts. For a standard actiCap layout, see acticap-64ch-standard2.mat.

dccn_customized_acticap64.mat

This is a custom 64-channel arrangement for the Donders Centre for Cognitive Neuroimaging (DCCN). It is based on a equidistant M10 cap and has electrode numbers rather than electrode names. The 32 channels from the 1st amplifier are located central, the 32 channels from the 2nd amplifier are along the rim, which means that electrodes preparation goes in outward moving circles.

dcc_customized_acticap64.mat

This is a custom 64-channel arrangement for the Donders Centre for Cognition (DCC). It is based on a 10-10 electrode layout, and uses two 32-channel EEG amplifiers. The green electrode holders correspond to the 32 channels from the 1st amplifier, and the yellow electrode holders correspond to the 32 channels from the 2nd amplifier. The reference and ground are included in the layout with the original name for the electrode location (TP9 and AFz).

mpi_customized_acticap64.mat

This is a custom 64-channel arrangement for the Max Planck Institute for Psycholinguistics (MPI). It is based on a equidistant M10 cap and has electrode numbers rather than electrode names. Note that the electrode positions are the same as for the DCCN customized version above, but that the channel order is different. The MPI version has the 32 channels from the 1st amplifier on the right and the 32 channels from the 2nd amplifier on the left, making it easier for two researchers to prepare the EEG cap on the subject simultaneously.

acticap-64ch-standard2.mat

This is the standard 64-channel actiCAP arrangement from Brain Products. It is based on the same coordinates as the EasyCap electrode caps. This particular layout was created using the easycapM1 layout and then removing eight electrodes (FPz, Iz, F9, F10, P9, P10, O9, O10) which are not present in the cap. Furthermore, two electrodes (AFz, FCz) were renamed to their purpose of being Ground (Gnd) and Reference (Ref) electrode.

BrainProducts R-Net

The following layout is for the 64-channel wet-sponge R-Net from BrainProducts.

BioSemi

The following template layouts are for BioSemi caps for active electrodes.

EasyCap

The following series of template layouts is for the electrode caps from EasyCap. They are sorted based on their electrode montages. FieldTrip provides .mat files (since r5201 - feb 2012) that are based on the bitmap images obtained from the easycap website and shown below. The layout structure stored in those .mat files contains fields that describe the position (.pos), the width (.width), and the height (.height), and the naming (.label) of the electrodes. Furthermore, it contains fields that describe the topographic interpolation boundaries (.mask) and the outlines of the ‘head’ (.outline).

EasyCap 10% arrangements

easycapM1 - 74-channel arrangement (used in EC80)

easycapM3 - Extended 10/20-System with 30 Channels

easycapM11 - 61-channel arrangement (“10%-System”) (used in BrainCap64)

easycapM15 - 128-channel arrangement

easycapM22 - Small Equidistant 29-channel arrangement (used in Braincap32)

easycapM23 - Large Equidistant 32-channel arrangement

easycapM24 - Large Equidistant 34-channel arrangement (used in EC40)

easycapM25 - International 10/20-System (used in EC20)

EasyCap triangulated equidistant arrangements

easycapM7 - Spherical 32-channel arrangement

easycapM10 - Equidistant 61-channel arrangement

easycapM14 - Spherical 124-channel arrangement

easycapM16 - Equidistant 88-channel arrangement

EasyCap miscellaneous arrangements

The following template layouts are provided

  • easycapM17.mat
  • easycapM20.mat
easycapM17 - 29-channel arrangement for Language Research

easycapM20 - BESA 32-channel arrangement for Epilepsy Diagnostics

EGI geodesic sensor nets

The following template layouts were created from the .sfp files that define the 3D electrode positions for EGI geodesic sensor nets. The code to generate these layouts is in fieldtrip/test/test_layout_egi.m.

NeuroScan Quick-Cap

The following template layouts are for electrode caps from NeuroScan. The origin and construction is described on http://bugzilla.fieldtriptoolbox.org/show_bug.cgi?id=679. The quikcap_nsl_128 layout has been kindly provided by Andre Cravo.

(since june 2012 - r6055)

(since nov 2012 - r6915)

MEG layouts

BTi/4D system

The following template layouts are for the sensor arrays of the BTi/4D MEG system.

With a more realistic display along the rim

CTF system

The following template layouts are for a sensor array of the CTF MEG system.

With a more realistic display along the rim

FieldLine OPM system

Alpha-1 smart helmet

Beta-2 smart helmet

Neuromag/Elekta/Megin system

306-channel system

with all channels

with only the magnetometers

with only the planar gradiometers

with the combined planar gradiometers

with a more realistic display along the rim, all channels

with a more realistic display along the rim, planar gradiometers only

with a more realistic display along the rim, planar gradiometers combined

with a more realistic display along the rim, magnetometers only

122-channel system

with the planar gradiometers

with the combined planar gradiometers

Yokogawa system

The following template layouts are for a sensor array of the Yokogawa MEG system. The labels in these layouts, except for the “old” variant, are prefixed to indicate the gradiometer type (PG - planar gradiometer, AG - axial gradiometer).

with only the axial gradiometers

with only the planar gradiometers

iEEG layouts (ECoG and sEEG)

Intracranial electrodes are in general placed according to a patient-specific implantation scheme, hence we don’t have general template layouts. The layout tutorial contains a specific section that shows various ways to make a layout for various sEEG and ECoG arrangements.

Furthermore, this section from the ft_prepare_layout help is of relevance.

% Alternatively you can specify the following options for systematic layouts which
% will be generated for all channels present in the data. Note that these layouts are
% only suitable for multiplotting, not for topoplotting.
%   cfg.layout = 'ordered'    will give you a NxN ordered layout
%   cfg.layout = 'vertical'   will give you a Nx1 ordered layout
%   cfg.layout = 'horizontal' will give you a 1xN ordered layout
%   cfg.layout = 'butterfly'  will give you a layout with all channels on top of each other
%   cfg.layout = 'circular'   will distribute the channels on a circle
%   cfg.width  = scalar (default is automatic)
%   cfg.height = scalar (default is automatic)
%
% For an sEEG shaft the option cfg.layout='vertical' or 'horizontal' is useful to
% represent the channels in a linear sequence . In this case you can also specify the
% direction of the shaft as going from left-to-right, top-to-bottom, etc.
%   cfg.direction = string, can be any of 'LR', 'RL' (for horizontal), 'TB', 'BT' (for vertical)
%
% For an ECoG grid the option cfg.layout='ordered' is useful to represent the
% channels in a grid array. In this case you can also specify the number of rows
% and/or columns and hwo the channels increment over the grid (e.g. first
% left-to-right, then top-to-bottom). You can check the channel order of your grid
% using FT_PLOT_LAYOUT.
%   cfg.rows      = number of rows (default is automatic)
%   cfg.columns   = number of columns (default is automatic)
%   cfg.direction = string, can be any of 'LRTB', 'RLTB', 'LRBT', 'RLBT', 'TBLR', 'TBRL', 'BTLR', 'BTRL' (default = 'LRTB')

NIRS layouts

Since NIRS caps are in general custom-made with the transmitter and receiver optodes over specific ROIs, we don’t have template NIRS layouts. The option cfg.layout = 'ordered' that is explained in the ft_prepare_layout help can be useful for a quick visualisation of all channels. The layout tutorial explains in general how to create your own channel layout for plotting, and we have a layout example specific to NIRS.

Plotting all layouts

You can use the following code to get a quick overview of the template layouts.

[ftver, ftpath] = ft_version;
dirlist = dir(fullfile(ftpath, 'template', 'layout', '*.*')); % here you can make a selection
filename = {dirlist(~[dirlist.isdir]).name}';

for i=1:length(filename)
  cfg = [];
  cfg.layout = filename{i};
  cfg.skipcomnt = 'yes';
  cfg.skipscale = 'yes';
  layout = ft_prepare_layout(cfg);

  figure
  ft_plot_layout(layout);
  title(filename{i}, 'Interpreter', 'none');

  [p, f, x] = fileparts(filename{i});
  print([lower(f) x '.png'], '-dpng');
  
  close all
end

After creating all bitmaps you can use ImageMagick on the Linux or macOS command-line to trim the whitespace.

for file in *.png ; do convert $file -trim $file ; done

You can find all template 2-D layouts for plotting here on GitHub.

These layouts are meant for plotting on a 2D screen or on paper using ft_topoplotER, ft_topoplotTFR, or any of the other high-level plotting functions explained in this tutorial. Furthermore, you can use them with the low-level ft_plot_topo function.

If you are looking for 3D positions of the EEG electrodes or MEG sensors to be used for forward modeling and inverse source reconstruction, or for more fancy 3D visualisation of the measured EEG potential over the scalp or MEG field distribution around the head using ft_plot_topo3d, you should look in the electrode template and gradiometer template documentation.