To elucidate the functional circuitry underlying the mechanisms of information processing in the brain, we need to monitor whole-brain activity changes when an animal displays a specific behavior or function, or how these patterns are upset in a neurological disorder. Therefore, a reliable method for analyzing the neuronal activity throughout the entire brain volume is essential.

Manganese-enhanced magnetic resonance imaging (MEMRI) or activation-induced manganese-dependent MRI (AIM-MRI) is one of the promising methods for investigating neuronal activities and neuronal pathways in the brain.

Mn2+ is a paramagnetic ion, which enhances MRI contrast by shortening the longitudinal relaxation time (T1) of H+. In AIM-MRI, Mn2+ is used as a surrogate marker of Ca2+ influx, since it can enter neurons through voltage-dependent Ca2+ channels and cannot be excreted by the Ca2+ extrusion mechanisms such as Na+/Ca2+-exchanger and Ca2+-ATPase. Mn2+ therefore accumulates in neurons in an activity-dependent manner. Thus, AIM-MRI can serve to non-invasively record the history of the neuronal activity.

Mn2+ is also known to be transported along axons and trans-synaptically to neighboring neuron in an anterograde manner, enabling direct monitoring of brain connectivity with laminar specificity. Thus, MEMRI tract-tracing is a valuable tool to study the rewiring of neuronal connections.

Taken together, MEMRI is proving useful as a new molecular imaging method to visualize functional neuronal circuits and anatomy in the brain in vivo. Moreover, AIM-MRI makes it possible to record the history of neuronal activity over the entire brain volume of animals in awake, freely moving condition, whereas blood-oxygen-level dependent (BOLD) functional MRI, which relies on blood hemodynamics, can only record the activity in head-fixed condition in the MRI scanner. MEMRI can be used for non-invasive investigation of whole brain activity and neuronal connections, which do not depend on blood hemodynamics but directly on neuronal activity. Therefore, MEMRI can be utilized for the study and diagnosis of various brain functions and neurological disorders.

In this Research Topic, we plan to generate a resource of the variety of MEMRI in neuroscience. Specifically, we plan to present original publications, methods, hypothesis & theory, and focused reviews relating to the following topics: Neuronal activity recordings with AIM-MRI, Neuronal tract tracing with MEMRI, as well as the fundamentals of MEMRI. While the scope of possible relevant topics is broad, the authors are encouraged to clearly indicate how their studies address the announced theme of MEMRI and AIM-MRI.

Important Note: All contributions to this Research Topic must be within the scope of the section and journal to which they are submitted, as defined in their mission statements. Frontiers reserves the right to guide an out-of-scope manuscript to a more suitable section or journal at any stage of peer review.