Friday Lunch Seminar (English)
September 30, 2022
12:15 〜 13:00
Talk Title: Quantitative activation-induced manganese-enhanced MRI (qAIM-MRI) can visualize the history of neural activities in the whole brain of a freely moving animal
Graduate School of Medicine
Host PI: Yoshichika Yoshioka
The brain has a complex hierarchical structure, and information is processed through interactions between and within hierarchies.
Therefore, directly linking phenotypes, the output results of the brain, to measurement results in one part of the brain involves a logical fallacy. This fallacy is called the mereological fallacy. To avoid this fallacy, we have constructed a multi-scale, multi-modal measurement system and applied it to neuroscience research. In the system, we employ quantitative activation-induced manganese-enhanced MRI (qAIM-MRI) as an in vivo noninvasive whole-brain neural activity measurement method.
Manganese ion (Mn^2+) can pass through calcium (Ca^2+) channels and is extruded very slowly from the cell. Ca^2+ channels open more frequently in highly active neurons; hence, in the presence of Mn^2+ in the extracellular solution, highly active neurons accumulate larger amounts of Mn^2+ than weakly active neurons. Therefore, Mn^2+ is a surrogate marker of Ca^2+ influx in excitable tissues. A paramagnetic ion, Mn^2+ shortens the longitudinal relaxation time (T1) of protons (H^+), and the longitudinal relaxation rate R1 (=1/T1) is proportional to Mn^2+ concentration. Thus, [Mn^2+] can be quantified by the R1 value calculated from the T1 value. Based on these ideas, AIM-MRI can use R1 to measure neural activity changes in a freely moving subject with the advantage of being insensitive to blood hemodynamics. In this seminar, I will show the Mn^2+ dynamics in the brain for optimizing the experimental protocols for AIM-MRI and will introduce some application results of AIM-MRI studies.