[Eeglablist] Is dipfit ever used for purposes other than localising source space data?

[Downey, Ryan J]

Copying the eeglablist in case my response is useful to anyone else.

Dipfit comes with a standard MRI scan built in. Of course it’s better to create your own model from a scan of the actual participant you are examining, but you can always use the generic MRI that’s readily available. Note that the boundary element model (MNI) is better than the four sphere model (BESA). The MNI is from an anatomical scan whereas the BESA is a simplified analytical model.

Besides either having a structural MRI of your own or using the generic MRI, you need to register the locations of your electrodes. That requires you either digitizing the locations before you collect EEG data or using estimated locations based on the known electrode montage you used. For example, if you used a 10-5 or 10-20 system, then you can have your channels listed as “Cz”, “Fz”, “Fp1”, “P3”, etc. and auto determine the locations based off the channel name. If the system doesn’t strictly follow the naming convention, then the manufacturer should have provided you with spherical or Cartesian coordinates of your generic electrode locations.


Ryan J. Downey
Postdoctoral Associate
Human Neuromechanics Laboratory
Biomedical Engineering Dept.
University of Florida


From: Kaelasha Tyler <kaelasha.tyler at gmail.com>
Sent: Monday, July 8, 2019 7:29 PM
To: Downey, Ryan J <RDowney at bme.ufl.edu>
Subject: Re: [Eeglablist] Is dipfit ever used for purposes other than localising source space data?

Hi Ryan,

Thanks for this.
If dipfit is only useful for source analysis and removing components of the ICA, then in that case I will just continue removing components by visual inspection and not use dipfit.

Dipfit requires anatomical information anyway doesn't it? (A structural mri) and I only have the eeg.

Cheers,
Kaelasha





On Tue, Jul 9, 2019 at 12:45 AM Downey, Ryan J <RDowney at bme.ufl.edu<mailto:RDowney at bme.ufl.edu>> wrote:
If you don't plan to use ICA at all then I can't think of any purpose of using dipfit.

If, however, you want to do analysis on channel data that has been cleaned by ICA, then you could potentially use dipfit. For example, you could run ICA on the data and then use dipfit to help you remove ICs that are artifacts and then finally reconstruct your channel level data with the bad ICs removed. But honestly, I would probably use visually assess the ICs rather than use dipfit to determine bad ICs. The reason being is that potentially you could have an ICA decomposition that wasn't perfect and contains an IC with two or more brain sources mixed together. This IC would have a bad dipole fit and could cause you to accidentally reject brain activity from your channel-level data. When cleaning channel data with ICA (i.e. not doing source analysis and clustering), I would err on the side of rejecting only ICs that are very obviously not brain (based on the spectra and time series plots) and keep ICs that could be mixtures of multiple neural sources or brain + noise.


Ryan J. Downey
Postdoctoral Associate
Human Neuromechanics Laboratory
Biomedical Engineering Dept.
University of Florida



-----Original Message-----
From: eeglablist <eeglablist-bounces at sccn.ucsd.edu<mailto:eeglablist-bounces at sccn.ucsd.edu>> On Behalf Of Kaelasha Tyler
Sent: Saturday, July 6, 2019 3:11 AM
To: eeglablist at sccn.ucsd.edu<mailto:eeglablist at sccn.ucsd.edu>
Subject: [Eeglablist] Is dipfit ever used for purposes other than localising source space data?

Hi all,

EEG and MEG data can be analysed at the level of electrodes/sensors, or on the data as it is reconstructed back into anatomical space in the brain, using are range of processes (Beamforming, dipole fitting, LORETA etc).

*My question is: will dipfit ever be useful if you are content carrying out the analysis at the level of the electrodes or sensors (not in reconstructed anatomical space)?*

To explain:
I am replicating an analysis in the literature, and reference in the paper I am following is made to fitting dipoles using dipfit2.2. However I am not needing to calculate eeg as it wold have occurred within the brain, but am content performing the analysis on ICA components of data recorded at the electrodes.

In this case, is there any need at all to fit dipoles using dipfit2.2 ?
Does using diptfit serve any other purpose?

Thanks in advance.
Kaelasha
_______________________________________________
Eeglablist page: https://urldefense.proofpoint.com/v2/url?u=http-3A__sccn.ucsd.edu_eeglab_eeglabmail.html&d=DwICAg&c=sJ6xIWYx-zLMB3EPkvcnVg&r=Xqv3i1MFyNQV9dhuL1e9BtqA0SbF1UWmfPtBzxDT0xY&m=P96U8QjH7uruFx5QkHdIhW3ew3qBznzGzuKFQ-GzCvE&s=8VJlLdKeX7vuE9AK9PP0rslLQy0-4gzcdxK8i7UpMZw&e=
To unsubscribe, send an empty email to eeglablist-unsubscribe at sccn.ucsd.edu<mailto:eeglablist-unsubscribe at sccn.ucsd.edu>
For digest mode, send an email with the subject "set digest mime" to eeglablist-request at sccn.ucsd.edu<mailto:eeglablist-request at sccn.ucsd.edu>