How does Trigger work with fNIRS? - Nirx

fNIRS experiments are most often based on the analysis of hemodynamic changes that occur as a result of behavioral changes (e.g. motor task performance) or changes in the environment (e.g. presentation of visual stimuli). Depending on the nature of the experiment, these changes can be either investigated in series (i.e. block-design) or individually (i.e. event-related design).

Independent of the experimental design chosen, it is important that the onset of stimuli is accompanied by a corresponding event marker, so that different behavioral or stimulus conditions can be distinguished from one another, and data analysis techniques can be used to assess whether accompanying hemodynamic changes statistically differ.

To correctly register the onset of behavioral and stimulus conditions, event markers have to be used. Event markers, oftentimes referred to as triggers, mark the period of time corresponding to the onset of the activity of interest. During data acquisition in NIRStar or Aurora, event markers will appear on the data recording screen as a dashed line. These markers will be stored in a trigger event file (NIRStar: *.evt file; Aurora: *_config.json file) which will be saved in the data folder of the recording.

The current document outlines the various possibilities of obtaining event markers in the data recorded by NIRx fNIRS instruments – both in terms of hardware as well as software options. Specifically, the following chapters cover how event markers can be added to the data manually, or by sending triggers using various types of hardware, by using specific software, or by using a combination of hardware and software.