[FieldTrip] Using Fieldtrip for LFP data analysis

[Fabyen Ragalmuto]

Dear Jan-Mathijs,

First of, thank you for your fast response! I am relatively new to working with Matlab, therefore excuse me if I pose some rather obvious questions.

My goal is to analyse the power spectra of local field potential data (recorded from a DBS system in the STN of patients) and compare this between certain conditions. I was planning on using a number of FieldTrip functions and build my analysis pipeline with these. Therefore, I wanted to use: ft_definetrial (optional) -> ft_preprocessing -> ft_freqanalysis -> ft_freqstatistics -> functions in order to visualise the results of these analyses. However, regardless of what functions I try to use and what I am inserting in the cfg structure, I always end up with the same error message:

Insufficient number of outputs from right hand side of equal sign to satisfy assignment.

Error in ft_version (line 154)
        ftver = tmp.Version;

Error in ft_preamble_init (line 50)
[FjmoT6aA_ft_ver, FjmoT6aA_ft_path] = ft_version;

Error in ft_preamble (line 83)
evalin('caller', full_cmd);

Error in ft_preprocessing (line 186)
ft_preamble init

Since I get the same error message using different functions, I would imagine it is caused by the data structure of the LFP data. Does the data have to be in a specific form in order to use the FieldTrip functions? Currently, the data is stored in a 1 x 13000 (depending on the length of the trial) double variable with a sampling frequency of 250hz. Each condition is stored in a separate variable.

I can also attach screenshots or parts of the script I used.

Best Regards
Fabyen


On 24. Mar 2021, at 12:16, Schoffelen, J.M. (Jan Mathijs) <jan.schoffelen at donders.ru.nl<mailto:jan.schoffelen at donders.ru.nl>> wrote:

Dear Fabyen,

Welcome on board! In order to be able to efficiently help you and put you on the right track, we probably need a little bit more information to go on.

The error you report is low-level matlab, suggesting that you (or matlab down the road) try/tries to do something like <some-output-arguments> = functionname(<some-input-arguments>).
Unless we know what you did exactly it’s all speculation, and hard to point you to a solution or to get you on your way. This would at minimum require you to mention what you try to do in more detail, and to provide us with a complete error stack.

However, note that data should not be implemented in a cfg structure.


Best wishes,
Jan-Mathijs


Dear FieldTrip discussion list,

I am a master student at the University of Amsterdam and for my research internship I have to analyse local field potential data. For that, I was planning on using the FieldTrip toolbox. However, when I try to implement my data in the cfg structure and use functions of the toolbox (such as ft_preprocessing and ft_freqanalysis) I always end up with the error: “Insufficient number of outputs from right hand side of equal sign to satisfy assignment.”. Does someone know why that might be the case or what kind of data structure is accepted in the FieldTrip functions?

I would appreciate it greatly if someone could help me with this issue!
Best Regards
Fabyen Ragalmuto
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