Source analysis (dipole fitting)
DIPFIT can be used to perform dipolar source analysis. See this Fieldtrip link for details.
Before performing dipole fitting, you must set channel coordinates, set a head model and set MRI data :
- Load channel coordinates
- Load head model
- Load MRI data
Dipoles can then be fitted to :
- Signals at a given latency
- Signals at event latencies (e.g. events marking ERP peaks)
- Scalp topographies of Independent Components (ICs)
###DIPFIT : Load channel coordinates
This function is used to define the channel coordinates for DIPFIT.
- Use standard MNI coordinates of the 10/05 electrode labels. Assign standard MNI coordinates to channels having standard International 10/05 labels.
- Load channel locations. Load a custom file with channel locations. This can be a file with individually-sampled channel coordinates.
###DIPFIT : Load head model
This function is used to define the head model.
- Load standard 3-shell MNI head model. Assign a standard 3-shell MNI head model.
- Load head model. Load a custom headmodel.
###DIPFIT : Load MRI data
This function is used to define the associated MRI data (for visualization).
- Load standard MNI MRI template. Assign a standard MNI MRI template.
- Load MRI data. Load a custom MRI data.
###DIPFIT : Fit dipole at a given latency
Fit dipole(s) at a user-define latency.
- Epoch. Select one or more epochs to display.
- Channel. Select one or more channels to display
- Index. Select the index to display (if >1).
- Y. Select the Y position to display.
- Z. Select the Z position to display.
- The dipole model can be either a Single dipole or Two symmetrical dipoles (symmetry in the X, Y or Z dimension), or Two unconstrained dipoles.
- The dipole fitting involves two steps, a coarse search using a grid, followed by a fine search. The Gridsearch resolution defines the resolution of the coarse grid search.
- Dipole label. The label to assign to the fitted dipole.
You may either fit at a selected latency, and use Set latency to define the latency. Alternatively, you can fit at a maximum within a range or fit at a minimum within a range, and set that latency range using Set lower latency limit and Set upper latency limit. The latencies can be defined by entering values in the corresponding fields, or clicking on the graph after clicking the Set latency radio button.
###DIPFIT : Fit dipole at event latency
Fit dipole(s) at event latencies. This is particularly useful if you have identified the latency of EEG responses (e.g. ERP peaks) using the Find peaks in waveforms function.
- Event code(s). Select the event code(s) onto which the dipole model should be fitted. The function will fit the dipolar model to the signals at each occurrence of the selected event code(s).
- The dipole model can be either a Single dipole or Two symmetrical dipoles (symmetry in the X, Y or Z dimension), or Two unconstrained dipoles.
- The dipole fitting involves two steps, a coarse search using a grid, followed by a fine search. The Gridsearch resolution defines the resolution of the coarse grid search.
- Dipole label. The label to assign to the fitted dipole.
###DIPFIT : Fit dipole onto IC topography
Fit dipole(s) onto IC topographies. This requires a dataset with an associated ICA matrix.
- ICs. Select the IC topography onto which the dipole model must be fitted.
- Plot IC topography. Plot the scalp topography of the selected IC.
- The dipole model can be either a Single dipole or Two symmetrical dipoles (symmetry in the X, Y or Z dimension), or Two unconstrained dipoles.
- The dipole fitting involves two steps, a coarse search using a grid, followed by a fine search. The Gridsearch resolution defines the resolution of the coarse grid search.