To intubate or not? Balancing anesthesia in rodent fMRI: strategies to mitigate confounding effects

More than a decade ago, the introduction of intubation and mechanical ventilation for performing blood oxygen level-dependent functional MRI studies in the rodent brain allowed an improved control over the physiological conditions during scanning sessions. An accurate understanding of respiratory parameters permits to respect the 3Rs in animal research, improves significantly the fMRI outcome, and promises improved translational studies. Developments also prompted a better comprehension on anesthetics and their impact on rodent brain physiology and function, bringing new insights on the buildup of carbon dioxide, interhemispheric connectivity, or arousal, which understanding are paramount for maturing better fMRI protocols in awake rodents. Despite many arguments in favor of intubation and subsequent mechanical ventilation, there are also many valid against it. Most importantly, the choice to intubate depends on the anesthesia protocol, where in some cases intubation is essential and impractical in others. This review does not advocate for one approach over the other. Instead, by examining the literature from the past two decades, we aim to provide a comprehensive review of the pros and cons of intubation and mechanical ventilation in fMRI studies, offering arguments for an informed decision tailored to the respective research question.