[FieldTrip] Value range of power from source analysis (eLORETA)

[Schoffelen, J.M. (Jan Mathijs)]

Hi Ina,

I see. Well, in that case I suggest that you need to study the eloreta code (and it’s lower level dependencies) in more detail to gain some more understanding (and to evaluate whether there’s something wrong witht he code). I never use this method myself so I don’t know the details of the implementation. You may want to be on the look-out for specific scaling operations that may assume certain units, or perhaps some differences in functional behavior with a higher-resolution input. If I recall correctly the eloreta is using an iterative scheme, which terminates upon ‘convergence’, or after a certain number of iterations. This might be different for the different inputs.

Best wishes,
Jan-Mathijs


On 28 Jun 2022, at 12:25, Ioana Susnoschi-Luca (PGR) via fieldtrip <fieldtrip at science.ru.nl<mailto:fieldtrip at science.ru.nl>> wrote:

Thank you for your quick reply Jan-Mathijs.
I was expecting something similar, but the opposite is true - higher values for higher resolution (i.e. more sources). Would that indicate I made a mistake in either one of the source models?

Ina
________________________________
From: Ioana Susnoschi-Luca (PGR)
Sent: 27 June 2022 22:18
To: fieldtrip at science.ru.nl<mailto:fieldtrip at science.ru.nl> <fieldtrip at science.ru.nl<mailto:fieldtrip at science.ru.nl>>
Subject: Value range of power from source analysis (eLORETA)

Hi everyone,

I was comparing my source analysis results for a source and leadfield model with resolution 1mm and one with resolution = 1cm and have noticed big differences in source-level power, as estimated with eLORETA. I am using the standard MRI from the Fieldtrip library.
In the case of res = 1mm, source power ranges between 1-15, while for res = 1cm, power values are much lower, 0.01-0.5. The sensor-level power (from ft_freqanalysis) ranges between 0.01-3.

When changing the model, I specified cfg.unit = 'cm' for the following functions: ft_prepare_headmodel, ft_prepare_sourcemodel, ft_prepare_leadfield. Is it possible I double-scaled somewhere?

Any indication of why this is the case or advice is very much appreciated!

Thanks,
Ina
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