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Mobile EEG-fNIRS – LiveAmp with actiCAP electrodes and NIRx NIRSport2

In this article, you will find resources specific to the combination of the LiveAmp with actiCAP and NIRSport2 from NIRx Medizintechnik GmbH. 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 NIRx NIRSport2 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 NIRSite 2.0 (NIRx montage design software) based on the 10-20 locations of your fNIRS optodes. These resources might be helpful:

2.2 Select the right cap 

For this combination, the caps that come with either of the systems are extremely comparable. In fact, both the actiCAP snap cap and the NIRx cap are manufactured by our sister company Easycap. Below you can find the full list of what you need for this step: 

  • actiCAP cap/NIRx cap (e.g., 128 slits, black fabric) 
  • EEG: actiCAP snap holders 
  • fNIRS: NIRSport2 cap holders 
  • fNIRS: Layer cap 

Figure 3. actiCAP cap with actiCAP snap holders for the EEG electrodes (10-20 montage) and NIRSport2 Grommet bases for the fNIRS (fronto-central montage). Inserting the holders follows a similar procedure to the one described in Figure 4 of the EEG-fNIRS cookbook

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: 

For the NIRx NIRSport2 cap, you can check the resources in the support center.  

3 Checking the signals 

Before starting with the data acquisition, we recommend checking the signals and eventually making some adjustments accordingly: 

4.2 Hardware triggers: triggering, synchronization, and acquisition  

A classical way of having event markers in both systems is to use hardware triggers that are generated by a single common source. Depending on your paradigm, your event markers might be generated by a presentation software (via USB port) or another hardware source (e.g., an LPT or BNC port from a response box). You can use the TriggerBox Plus to receive event markers from different sources and forward them, with millisecond precision, to target devices. In this case, the target devices are the EEG amplifier and the fNIRS. For this reason, we need a way of sending the event markers to both.

Below you will find different options to do so. These include: 

  • LSL (Lab Streaming Layer) 
  • Wireless Triggering (1 Transmitter to 2 Receivers) 
  • Trigger Mirroring 

4.1 Triggering and event synchronization via LSL 

For triggering and event synchronization between LiveAmp and NIRSport2 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 NIRSport2 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 NIRSport2, you can connect to LSL directly from Aurora (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 Aurora.  

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 NIRSport2, you can monitor the data and the LSL markers directly in Aurora. 

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 to acquire only the LiveAmp data together with the LSL markers and use Aurora to acquire fNIRS and LSL markers.  

4.2 Adding the STE: more shared triggering options 

If you have a Sensor and Trigger Extension, then you can also take advantage of the Wireless Trigger and Trigger Mirroring functionality.  

4.2.1 Trigger mirroring

If you have a Sensor and Trigger Extension, you can use the Trigger-out DSUB-9 F port to forward the incoming triggers to the NIRSport2. This is made possible by the trigger mirroring function, which can be activated in BrainVision Recorder with only a few clicks (Figure 8).  

EEG-fNIRS LiveAmp with NIRx fNIRS

Figure 8. Trigger Mirroring implementation in Recorder for LiveAmp with Sensor & Trigger Extension. 

Your event markers will be automatically forwarded from the EEG to the fNIRS device, without any significant delay, given the slower sampling rate of the fNIRS. Now, if you add our Wireless Trigger to this setup, you can have a fully-mobile EEG-fNIRS set-up with wireless hardware sharing. 

Figure 9. Trigger Mirroring implementation with LiveAmp, STE, and NIRsport2

4.2.2. Wireless Trigger (only for LiveAmp with STE)

Another option, if you do not want to use the Trigger Mirroring, would be to take advantage of the fact that our Wireless Trigger for LiveAmp STE can send triggers from one Transmitter to multiple receiving units (described here). Now, since the NIRSport2 can receive TTL pulses from an LPT connector port, it can theoretically be equipped with a Wireless Trigger Receiver. All you need is an adapter cable (DSUB9 to LPT) and a USB to DC power adapter (available at Easycap: KB-USB-DC0,65) and a USB power bank.  

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