Functional Brain Analysis with Near-Infrared Spectroscopy

Significance of the Topic

Functional near-infrared spectroscopy (fNIRS) has emerged as a versatile, noninvasive brain-imaging technique that measures changes in cerebral hemoglobin concentrations by detecting scattered near-infrared light. It offers unique advantages over EEG, fMRI, PET and MEG, including fewer constraints on subject posture and movement, high temporal resolution (sub-100 ms), and compatibility with other modalities. These features make fNIRS especially valuable for cognitive neuroscience, neurorehabilitation, psychiatry, neuroergonomics and brain-machine interface research.

Goals and Overview of the Study

This application note by Shimadzu presents the principles, instrumentation and application examples of fNIRS in functional brain analysis. It provides a comparative overview of common brain-imaging methods, introduces Shimadzu’s LABNIRS multi-channel system, and illustrates applications ranging from motor control and neurorehabilitation to simultaneous EEG/fMRI measurements, linguistic processing, inner speech detection and mental-health diagnostics.

Methodology and Used Instrumentation

Functional brain-function imaging with fNIRS relies on three infrared wavelengths (780, 805, 830 nm) to distinguish oxygenated (Oxy-Hb) and deoxygenated hemoglobin (Deoxy-Hb). Light emitted through fiber-optic probes penetrates scalp, skull and cortex before being scattered and captured by receiver fibers. Shimadzu’s LABNIRS system supports up to 142 channels, high-density or standard probe distributions, and temporal resolution as fast as 6 ms per channel.

Used Instrumentation

• LABNIRS functional near-infrared spectroscopy system with FLASH (Flexible Adjustable Surface Holder)
• Multi-channel holders for frontal, temporal, parietal or whole-head measurements
• Optional modules: EEG simultaneous-measurement holder, MRI-fusion software, real-time data transfer, 3D position measurement, stimulus presentation, video recording
• Photomultiplier-tube detectors for high-sensitivity measurements

Main Results and Discussion

• Neurorehabilitation: fNIRS can image cortical activation during dynamic tasks (walking, obstacle avoidance) that are inaccessible to fMRI or PET, enabling assessment of hemiplegic gait and rehabilitation outcomes.
• fMRI Comparison: fNIRS Oxy-Hb/Deoxy-Hb maps correspond with fMRI BOLD signals during motor tasks and reveal additional metabolic information, useful in patients with implants or movement limitations.
• Motor Control: Task-related increases in prefrontal and sensorimotor cortex activity have been recorded during posture control, walking, arm reaching (including prism adaptation) and graded muscle force tasks.
• Simultaneous EEG: Whole-head fNIRS combined with 32-channel EEG captures hemodynamic and electrophysiological responses to median-nerve stimulation, clarifying neurovascular coupling.
• Signal Analysis: A wavelet-based multiresolution approach and z-score standardization enhance detection of task-related hemoglobin fluctuations and produce brain-activity maps comparable to fMRI during cognitive tasks.
• Inner Speech: By comparing 7 mm (scalp) vs. 18 mm (cortical) probe spacings and monitoring EMG and skin blood flow, fNIRS can detect transient frontal- lobe activation during silent speech and distinguish it from muscle or skin artifacts.
• Language Processing: In Chinese–Japanese bilinguals, fNIRS in dorsolateral prefrontal cortex reveals differential left-hemisphere inhibition of the non-target language and right-hemisphere engagement for target-language attention.
• Mental-Health Research: Verbal-fluency tasks yield distinct Oxy-Hb patterns in unipolar depression vs. bipolar disorder. Novel indices (area under curve, weighted-center latency) differentiate patient groups and may improve diagnostic monitoring.

Benefits and Practical Applications

• Noninvasive, portable and safe measurement in naturalistic environments
• High temporal resolution for rapid hemodynamic changes
• Flexibility to study active tasks, bedside monitoring and pediatric subjects
• Multimodal integration with EEG, fMRI, video, stimulation and neurofeedback systems

Future Trends and Possibilities

Emerging developments include wearable and wireless fNIRS devices for real-world brain monitoring, integration with brain-machine interfaces and neurofeedback protocols, high-density diffuse-optical tomography, advanced signal-processing algorithms and multimodal fusion with MRI/EEG/MEG to elucidate brain networks in health and disease.

Conclusion

Shimadzu’s fNIRS technology provides a powerful, flexible platform for functional brain analysis across basic neuroscience, clinical research and applied engineering. Its ability to noninvasively monitor hemodynamics in freely moving subjects, combined with modular expandability, positions fNIRS as an essential tool for next-generation brain-function studies.

References

• Shimodera S, Imai Y, Kamimura N, et al. (2012) Near-infrared spectroscopy of bipolar disorder may be distinct from that of unipolar depression and of healthy controls. Journal of Affective Disorders 4(4):258–265.
• Miyai I, et al. (2004) Application of fNIRS in Neurorehabilitation. MEDICAL NOW, No. 52:33–36.
• Takeuchi M, et al. (2009) Brain cortical mapping by simultaneous recording of fNIRS and EEG during right median nerve stimulation. Brain Topography 22:197–214.