Mobile EEG-fNIRS – LiveAmp with actiCAP electrodes and Artinis Brite

In this article, you will find resources specific to the combination of the LiveAmp with actiCAP slim electrodes and Artinis Brite fNIRS. The information covered here, should be used together with the main EEG-fNIRS Cookbook. The section numbers used here correspond to the sections in the EEG-fNIRS Cookbook.

Figure 1. Brain Products LiveAmp and Artinis Brite for mobile neurophysiological studies. 

2.1 Defining your EEG-fNIRS montage 

The channel positions for your EEG cap can be downloaded from the Brain Products website (.bvef format). These locations then can be loaded into either BrainVision Recorder  when setting up the workspace or into your offline analysis software at a later stage. 

The fNIRS montage can be selected from the list of predefined templates in OxySoft. Using the Optode Template Editor (OTE) it is also possible to create customized templates, either from scratch or by choosing from existing ones. These templates can be added to your template library in OxySoft.  

Additionally, OxySoft supports digitization of the optodes’ locations on the headcap, providing MNI coordinates of the optodes. This digitization can be done manually or using a digitizer (see this video for a quick overview). 

2.2 Selecting the right cap 

For this combination, you have the freedom to choose from two types of caps depending on whether you prefer to have the same type of cap you would normally use with your LiveAmp or with your Brite. 

Option 1:  

• actiCAP cap (e.g., 128 slits, black fabric) 
• EEG: actiCAP snap holders 
• fNIRS: Brite optode holders (make sure that inter-optode distances are approximately 3 cm) 

Figure 2. actiCAP cap with actiCAP snap holders for the EEG electrodes (10-20 montage) and Brite optode holders for the fNIRS (occipital montage). Inserting the holders follows a similar procedure as the one described in Figure 4 of the EEG-fNIRS cookbook. 

Option 2:  

• Artinis neoprene headcap*  
• EEG: actiCAP snap holders for Artinis headcap (available at Artinis)
• fNIRS: Brite optode holders  

* All Artinis headcaps have printed NIRS optode marks in a grid of 30 mm and indicators for the EEG 10/20 system. Artinis offers headcaps with and without pre-made holes. The caps with pre-made holes are made using a 30 mm grid. Some of these holes may overlay the 10-20 standard locations. If the preference is to use the exact 10-20 positions, then one can punch holes for both fNIRS and EEG at the desired locations in the headcap with no premade holes (see this video). 

Figure 3. Artinis headcap with actiCAP snap holders for Artinis headcap for the EEG electrodes and Brite optode holders for the fNIRS (with pre-frontal and central montage). Keep in mind that the actiCAP snap holders for Artinis headcap (in order to be used flexibly on the cap) do not have a channel number label.  

2.3 Populate the cap 

Once the holders are on the cap, you will need to add the sensors.  

For actiCAP electrodes, you can check these two resources, which contain important information on how to handle the electrodes and how to optimize their placement on the head for the best signal quality and user experience: 

• actiCAP slim active electrodes walkthrough  
• How to avoid cable spaghetti – Our tips and tricks to nicely setup your actiCAP snap cap 

For the Artinis cap you can have a look at these two guides explaining which headcap to select, as well as the co-placement of fNIRS optodes and EEG electrodes.  

• fNIRS headcaps
• Multimodal fNIRS-EEG measurements — Integration on the head

3 Checking the signals 

Before starting with the data acquisition, we recommend checking the signals and making adjustments accordingly. 

For the EEG, you should check the impedance levels in BrainVision Recorder (see this detailed description or check this video).  

For the fNIRS, you can check the signal quality in OxySoft based on the amount of light received in the Template DAQ values window. The corresponding state for each channel can also be monitored in the Template DAQ state window (Figure 4). Additionally, Artinis implemented a Signal Quality Index (SQI) which categorizes the signal quality in three levels: bad, medium and good. For more information you can refer to this resource. 

Figure 4. Updated user interface in the Template DAQ state window of OxySoft 4.0 indicating good and bad signal quality

Furthermore, Brite comes with a multipower gain control function that adjusts light intensity per channel based on their current state. This power optimization is always automatically performed at the start of a measurement. If, after this step, there are still bad channels, you can follow the guidelines described in the device manual to further improve the signal.

4.1 Triggering and event synchronization via LSL 

For triggering and event synchronization between LiveAmp and Brite you can use LSL. To do so, you will have to follow these steps. 

4.1.1 Create a network

Make sure that your local network is running and the two computers on which your LiveAmp and your Brite are being operated are mutually discoverable.  

4.1.2 Connect the streams to LSL

This step needs to be done separately for the two devices and the LSL markers. For the LiveAmp, you can use the LiveAmp LSL connector, downloadable for free from our GitHub page. 

Keep in mind that the LiveAmp LSL connector cannot check impedances!  

For this reason, first reduce the impedance of the actiCAP slim electrodes via BrainVision Recorder (click here for a detailed description or check this video). Then, disconnect the LiveAmp from with BrainVision Recorder, open the LiveAmp LSL connector app, search for the device, and hit “Link” (more a thorough description check this blog post). 

For the Brite, you can connect to LSL directly from OxySoft, by navigating to Data Collection > LSL Mapping (see Figure 4 below) and then follow the instructions in this video tutorial.  

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Figure 4. Connecting the Brite to LSL via OxySoft.

For the LSL markers you have two options, depending on whether you want to edit your experiment script by adding new LSL-specific code or not:  

• With code – in E-Prime^®, Presentation^®, MATLAB^®, or Python, you can check this resource
• Without code – use the TriggerBox Plus, which offers a one-button solution to convert your existing triggers into LSL markers

4.1.3 Monitoring the LSL streams

The LSL data streams will have to be monitored in separate software solutions:  

• For the LiveAmp, you can use our BrainVision LSL Viewer to monitor EEG and LSL markers (refer to the EEG-fNIRS cookbook). 
• For the Brite, you can monitor the data and the LSL markers directly in OxySoft. 

4.1.4 Recording the LSL streams

Depending on your preferences, you can use LabRecorder.exe to acquire all the data into an XDF file. During the offline processing, you can then extract the EEG and LSL markers, as well as the fNIRS data with the LSL markers, and process them separately. Alternatively, you can use LabRecorder.exe to acquire only the LiveAmp data together with the LSL markers and use OxySoft to acquire the fNIRS data and LSL markers.