Neural activity raises oxygenated and lowers de-oxygenated blood locally, enabling optical imaging

Evidence

Near infra-red (NIR) light (wavelengths 650–1000 nm) is relatively transparent to human tissues. The absorption spectra of oxygenated and de-oxygenated haemoglobin (HbO and HbR respectively) for NIR light differ in that HbO maximally absorbs light of longer wavelength (900–1000 nm) whereas HbR maximally absorbs light of shorter wavelength. These differential absorption spectra make it possible to separate out changes in the concentration of HbO and HbR. In response to neural activity in the brain, an increase in oxygenated blood is directed to the region, resulting in a drop in de-oxygenated blood. Thus HbO and HbR concentrations change in opposite directions in response to neural activity (Shah and Seghouane 2014 ). Changes in HbO and HbR resulting from a neural response to a stimulus or due to resting state activity can be analysed to produce activation patterns and also to derive connectivity measures between regions of interest. — Dijk, Pim van, Physiology, Psychoacoustics and…, 4282

Categorization

• DEFINE: Explains the hemodynamic basis (HbO/HbR opposites) that underpins all fNIRS measures.
• XREF: Connects to fMRI BOLD-neurovascular coupling literature; both rely on the hemodynamic response following neural activity.