Mobile EEG-fNIRS – LiveAmp with actiCAP electrodes and Cortivision Photon

In this article, you will find resources specific to the combination of the LiveAmp with actiCAP slim electrodes with the Photon fNIRS from Cortivision. 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 Cortivision Photon 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 either into BrainVision Recorder when setting up the workspace or into your offline analysis software at a later stage.

The fNIRS montage can be defined in CortiView based on the 10-5 locations of your fNIRS optodes (Figure 1). For an extensive overview of other tools that can be used for designing the fNIRS channel array, you can check this resource on Cortivision’s website). 

Figure 2. fNIRS montage settings in CortiView. 

2.2 Select 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 Photon. 

Option1:  

• actiCAP cap (e.g., 128 slits, black fabric), 
• EEG: actiCAP snap holders 
• fNIRS: Photon cap holders 
• fNIRS: Layer cap** 

Inserting the holders follows a similar procedure to the one described in Figure 4 of the EEG-fNIRS cookbook.

Option 2:  

• Photon cap*  
• EEG: actiCAP snap holders 
• fNIRS: Photon cap holders 
• fNIRS: Layer cap** 

* The cap comes with 128 positions according to the 10-5 system with additional holes for hair management. This type of cap is comparable to the neoprene cap that comes with the Brain Products actiCAP Xpress Twist. 

** For better contact of optodes/ electrodes with the skin and to keep the cables in the same position

Figure 3. Photon cap with actiCAP snap holders for the EEG electrodes and Photon optode holders for the fNIRS.  

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 Cortivision Photon cap, you can check the dedicated videos on Optodes mounting and on Putting on a cap. 

3 Checking the signals 

Before starting with the data acquisition, we recommend checking the signals and eventually make some 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 contact quality in CortiView (click here for a detailed description or check this video). You can also refer to this resource for a more dedicated discussion on data quality. 

4.1 Triggering and event synchronization via LSL 

For triggering and event synchronization between LiveAmp and Photon 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 Photon 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 Photon, you can connect to LSL directly from CortiView (General settings > Advanced Settings tab), by checking the Lab Streaming Layer box and, eventually, editing the stream name (see Figure 4).  

Figure 4. Enabling LSL in CortiView.  

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 – for example, 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 Photon, you can monitor the data and the LSL markers directly in Cortiview. 

4.1.4 Recording the LSL streams

Depending on your preferences, you can use LabRecorder 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 Cortiview to acquire fNIRS and LSL markers.