Stimulation delays

1

Hi

I have to adjust my triggers for stimulation delays. I saw the option for doing this through Brainstorm (Events>time offset) but this seems to require the same offset correction across trials. I have data from a cognitive task which has 4 categories (original_11, original_12, original_21 & original_22), each with a 100 trials so a total of 400 trials per subject. The offset delay varies from trial to trial. Could you advise how I can amend individual trials?

I have the delay for each trial for each subject stored in a table 'T'. T.Subject has all subject IDs (400 rows for each subject), T.Conditions has the categories (11, 12, 21 & 22 (100 rows per category)), T.Trial lists the number of the trial in each category (1-100) and T.Delay has all the delays that the 'original' time stamp has to be corrected for. I looked at doing this through MatLab but I'm not sure how to match between a table and a struct so trials are altered appropriately?

sFiles = bst_process('CallProcess', 'process_select_search', sFiles, [], ...
'search', '(([name CONTAINS "resample"]))');
for iFile = 1:length(sFiles)
DataMat = in_bst_data(sFiles(iFile).FileName);

original_11 = DataMat.F.events(1).times
original_12 = DataMat.F.events(2).times
original_21 = DataMat.F.events(5).times
original_22 = DataMat.F.events(6).times

end

sample rows form T
T =
Subject Conditions Trial Delay
"Subject008" 11 95 83
"Subject121" 12 96 84
"Subject156" 21 97 67
"Subject356" 22 98 67

2

This is too specific to handle it from the interface.
The easiest and most efficient solution is probably write a script that edits directly the events structure from the original continuous file:
https://neuroimage.usc.edu/brainstorm/Tutorials/Scripting#Example:_Editing_events

Events structures are documented here:
https://neuroimage.usc.edu/brainstorm/Tutorials/EventMarkers#On_the_hard_drive

3

Hi Francois,

Thank you. I will try developing a script using these sources. Reading through that material and looking at other sources/forums for MatLab I'm not sure how to 'match' variables between the table and struct e.g. match subject, event category and trial. Could you advise what function I should look at for this?

4

If you are comfortable with Matlab programming, you should start by looking for Matlab tutorials teaching you how to write for loops, if/else tests and strcmp/strcmpi for testing the equality between two strings.

5

Hi

This script allowed me to add delays to individual trials. I ran this after running a script to create a new event with offset as in the tutorial to edit events (link below). I had an Excel file (delay_triggers), with four columns for subject ID, event categories (I had four categories, below is for one), trial number within event category and delays (in ms).

https://neuroimage.usc.edu/brainstorm/Tutorials/Scripting#Example:_Editing_events

t = readtable('delay_triggers')

[testID, SubjectNames] = findgroups(t.Subject);
[testID, Events] = findgroups(t.Event);
Events = num2cell(Events)

% create struct for delays

for i = 1:length(SubjectNames)
for i2 = 1:length(Events)

B(i).Subject = string(SubjectNames(i))
B(i).Events = Events
B(i).Events(i2,2) = {zeros(1,100)}

end

end

% add delays to struct

for i = 1:length(SubjectNames)
for i2 = 1:length(Events)

b = (ismember(t.Subject, B(i).Subject)) & (ismember(t.Event, B(i).Events{i2})) 
idx = find(b) 
B(i).Events(i2,2) = {t.Delay(idx)}
   
  end

end

% add delays to events in Brainstorm

for i = 1:length(RawFiles)

    sRaw = in_bst_data(RawFiles(i).FileName, 'F');

for i2 = 1:length(B)

if contains(string(sRaw.F.filename),B(i2).Subject)

sRaw.F.events(iEvtNew11).times(1,:) = sRaw.F.events(iEvtNew11).times(1,:) + B(i2).Events{1, 2}'
  
  end   
   end

sRaw.F.events(iEvtNew11).times = ...
round(sRaw.F.events(iEvtNew11).times .* sRaw.F.prop.sfreq) ./ sRaw.F.prop.sfreq;

bst_save(file_fullpath(RawFiles(i).FileName), sRaw, 'v6', 1); % saves modifications on data file in Brainstorm database

end