Neuroimaging in Addiction: Principles of Functional Near-infrared Spectroscopy and Its Emerging Role in De-addiction: A Narrative Review.

BACKGROUND: Substance use disorders (SUDs) remain a major global health challenge with high relapse rates. Functional near-infrared spectroscopy (fNIRS), a non-invasive, portable modality enabling real-time monitoring of cortical haemodynamic changes, is well suited to studying addiction neurobiology in ecologically valid settings. This review examines fNIRS principles and applications in addiction research and de-addiction therapy. SUMMARY: PubMed, Scopus and Web of Science were searched (2000-2025) using terms including fNIRS, addiction, substance use disorder, prefrontal cortex, neurofeedback and de-addiction. fNIRS reliably detects altered prefrontal cortex (PFC) haemodynamic responses during cue-reactivity and cognitive tasks in addiction. Findings include reduced dorsolateral PFC activation with prolonged abstinence, differential orbitofrontal cortex activation across substances, and use as a treatment-response biomarker. Emerging applications include neurofeedback and machine-learning-based classification. fNIRS offers portability and ecological validity over conventional neuroimaging. Future research should standardise protocols, validate biomarkers in multicentre trials, and integrate fNIRS with EEG and fMRI. KEY MESSAGE: fNIRS is a portable, non-invasive tool that reliably detects altered prefrontal cortex activation in substance use disorders. Cue-reactivity and cognitive paradigms identify biomarkers of craving, executive dysfunction and relapse risk. fNIRS-based neurofeedback shows early promise for improving self-regulation and reducing relapse. Wearable fNIRS with machine learning and multimodal integration enables personalised addiction monitoring.