Link between respiration depth, hemodynamic responses and neural activity in awake, behaving, non-human primates

Functional near-infrared spectroscopy (fNIRS) has become a growing technology for measuring brain activity and diagnosing and monitoring neurological diseases. However, fNIRS relies on the assumption of intact neurovascular coupling (NVC). We have observed that mean arterial blood pressure (MAP) can lead to changes in fNIRS readings. Understanding how healthy fluctuations in MAP, for instance due to respiration, can influence NVC is important to understand disease. In order to do this, we trained one non-human primate (NHP) to perform a fixation task while measuring hemodynamics (fNIRS), neural activity (intracortical arrays in visual cortex), and respiration. We showed a significant increase in ∆HbO with higher respiration depth and a significant decrease in local field potential (LFP) envelope with increased respiration depth. However, no significant relationship was found between respiration depth and the hemodynamic response function (HRF) estimation. These findings suggest that respiration depth affects hemodynamic responses and neural activity, but further research is is needed to understand the link between respiration and induced changes in neural and vascular signals.