# Dealing with stimulation artefacts¶

Sometimes, because of external stimulation, you may end up having some artefacts on top of your recordings. For example, in case of optogenetic stimulation, shinning light next to your recording electrode is likely to contaminate the recording. The code has a built-in mechanism to deal with those artefacts, in the triggers section of the parameter file. In a nutshell, the code will, from a list of stimulation times, compute the average artefact, and substract it automatically to the signal during the filtering procedure.

## Specifying the stimulation times¶

In a first text file, you must specify all the times of your artefacts, identified by a given identifier. The times can be given in ms or in timesteps, and this can be changed with the trig_unit parameter. By default, they are assumed to be in ms. For example, imagine you have 2 different stimulation protocols, each one inducing a different artefact. The text file will look like:

0 500.2
1 1000.2
0 1500.3
1 2000.1
...
0 27364.1
1 80402.4


This means that stim 0 is displayed at 500.2ms, then stim 1 at 1000.2ms, and so on. All times in the text file are in ms, and you must use one line per time. Use trig_unit if you want to give times in timesteps.

## Specifying the time windows¶

In a second text file, you must tell the algorithm what is the time window you want to consider for a given artefact. Using the same example, and assuming that stim 0 produces an artefact of 100ms, while stim 1 produces a longer artefact of 510ms, the file should look like:

0 100
1 510


Here, again, use trig_unit if you want to provide times in timesteps.

## How to use it¶

Once those two files have been created, you should provide them in the [triggers] section of the code (see here). Note that by default, the code will produce one plot by artefact, showing its temporal time course on all channels, during the imposed time window. This is what is substracted, at all the given times for this unique stimulation artefact.

Example of a stimulation artefact on a 252 MEA, substracted during the filtering part of the algorithm.

Note

If, for some reasons, you want to relaunch this step (too small time windows, not enough artefacts, ...) you will need to copy again the raw data before relaunching the filtering. This is because remember that the raw data are always filtered on-site.