Concurrent fNIRS and transcranial magnetic stimulation (TMS) allows for direct investigation of cortical brain activation and connectivity. Moreover, the effects of repetitive TMS (rTMS) in distinct brain regions without quantifiable behavioral changes can be objectively measured through fNIRS.
Since fNIRS does not use of electrical (nor magnetic) fields, it is suitable to be combined with TMS without particular technical precautions. Furthermore, as NIRS is an optical signal, the strong magnetic fields generated during TMS do not cause artifacts or interference in the NIRS data. The TMS coil may therefore be placed directly over NIRS probes, making it possible to measure hemodynamic changes directly under the stimulated site.
NIRS: A technique for Neuroimaging during TMS - promising NIRS-TMS applications
Compared to many modalities, NIRS is still relatively new. More studies are needed in the field of concurrent fNIRS and TMS, but all indications suggest that this combination would be beneficial for a variety of different applications:
Advantages and Considerations for NIRS-TMS studies
Combining NIRS with TMS has several advantages including the absence of electromagnetic interference from the TMS pulse to the optical signal, better temporal resolution than fMRI or PET, small and portable imaging equipment. However, several technical considerations are important:
Left: The NIRx NIRScap with integrated TMS optodes. The optodes are completely compatible with TMS stimulation. Their low profile allows for very close placement of the TMS coil.
Right: The NIRx TMS compatible overcap, placed over the NIRScap. The retaining cap stabilizes the setup making it more robust to TMS coil contact artifacts and motion artifacts in general.
NIRScout is an ultra-compact fNIRS neuroimaging solution that offers the versatility and scalability to fit a broad range of research applications. For example, investigating motor sensory functions, traumatic brain injury, learning/attention disorders and brain computer interfaces.
NIRSport is the first freely configurable, wearable, multichannel NIRS imaging system to be used on any part of the head. This pocket-book sized device combines LED illumination and innovative active detection technology into a truly wearable brain imaging solution.