Using fNIRS for Prefrontal-Asymmetry Neurofeedback: Methods and Challenges

Functional near-infrared spectroscopy (fNIRS) has become increasingly accessible in recent years, which allows this relatively lowcost and portable brain sensing modality for the application of braincomputer interfaces (BCI). Although there is a growing body of research on fNIRS-based BCI utilising users’ covert psychophysiological activity, there is comparably less research on active BCI, where users engage in thinking strategies with the explicit intention of controlling the behaviour of an interactive system. We draw on four empirical studies, where participants received real-time neurofeedback (NF) of left-asymmetric increase in activation in their dorsolateral prefrontal cortex (DL-PFC), which has previously been identified as a correlate of approach-related motivational tendencies. We discuss methodological considerations and challenges, and provide recommendations about brain-signal selection and integration, NF protocol design, post-hoc and real-time applications of NF success criteria, continuous visual feedback, and individualised feedback based on the variations of the brain-signal in a reference condition.