Applications of Functional Near-Infrared Spectroscopy (fNIRS) in Monitoring Treatment Response in Psychiatry: A Scoping Review

Abstract

Background/Objective: Functional near-infrared spectroscopy (fNIRS) is a non-invasive neuroimaging technique with growing relevance in psychiatry. Its ability to measure cortical hemodynamics positions it as a potential tool for monitoring neurofunctional changes related to treatment. However, the specific features and level of consistency of its use in clinical psychiatric settings remain unclear. A scoping review was conducted under PRISMA-ScR guidelines to systematically map how fNIRS has been used in monitoring treatment response among individuals with psychiatric disorders. Methods: Forty-seven studies published between 2009 and 2025 were included based on predefined eligibility criteria. Data was extracted on publication trends, research design, sample characteristics, fNIRS paradigms, signal acquisition, preprocessing methods, and integration of clinical outcomes. Reported limitations and conflicts of interest were also analyzed. Results: The number of publications increased sharply after 2020, predominantly from Asia. Most studies used experimental designs, with 31.9% employing randomized controlled trials. Adults were the primary focus (93.6%), with verbal fluency tasks and DLPFC-targeted paradigms most common. Over half of the studies used high-density (>32-channel) systems. However, only 44.7% reported motion correction procedures, and 53.2% did not report activation direction. Clinical outcome linkage was explicitly stated in only 12.8% of studies. Conclusions: Despite growing clinical interest, with fNIRS showing promise as a non-invasive neuroimaging tool for monitoring psychiatric treatment response, the current evidence base is limited by methodological variability and inconsistent outcome integration. There is a rising need for the adoption of standardized protocols for both design and reporting. Future research should also include longitudinal studies and multimodal approaches to enhance validity and clinical relevance.

Keywords: brain activation scoping review; functional near-infrared spectroscopy; neuroimaging; psychiatric disorders; treatment monitoring; treatment response.

Figure 1

PRISMA flow diagram showing included studies at each stage of the inclusion/exclusion process.

Figure 2

Annual distribution of fNIRS publications on monitoring treatment response in psychiatric populations.

Figure 3

Age distribution across studies.

Figure 4

Use of fNIRS to Monitor Treatment Response Across Psychiatric Disorders. (A) Heatmap showing the number of studies employing fNIRS across different psychiatric diagnoses and intervention types. Most research has focused on MDD, schizophrenia, and anxiety disorders, particularly in conjunction with rTMS/iTBS and pharmacological interventions. (B) Sankey diagram illustrating the flow from diagnosis to intervention and reported clinical outcomes. The majority of studies report positive fNIRS-clinical correlations, though representation varies across disorders. Gaps in combined or VR-based therapies suggest potential avenues for future research.

Figure 5

Bubble plot to illustrate fNIRS use to monitor treatment-related brain activation in relation to symptom improvement across psychiatric studies (N = 47). The x-axis represents the number of studies reporting each combination of activation pattern and clinical link, while the y-axis categorizes the direction of fNIRS activation observed post-treatment: increased, decreased, mixed, or not reported. Each bubble is sized according to sample size category, ranging from single-subject designs to studies with over 100 participants. Bubble color indicates whether a link between fNIRS signal change and clinical improvement was reported (Yes = blue, No = red, Not reported = grey).