Developed in the 1990s, functional magnetic resonance imaging (fMRI) has revolutionized the study of the brain. But the measurement of cerebral activity remains indirect – blood oxygenation is measured – which limits spatial resolution to a few millimeters and temporal resolution to around one second. A Korean team, led by Jan-yeon Park (Sungkyunkwan University, Suwon), proposes, in Science of October 14, a new direct method of imaging neuronal activity using fMRI, allowing finer visualization in vivo of the activity of a chain of neurons on 0.22 mm slices of brain, over a time window of only five milliseconds. Denis Le Bihan (CEA Neurospin), a pioneer in functional imaging, greets a “tour de force”but questions the extension to humans of this technique, which presupposes perfect immobility.
Unprecedented spatio-temporal resolution
Using a functional MRI device (IRMF) with different data processing, a Korean team is testing a new method of direct imaging of neuronal activity (Diana, in English) in anesthetized mice.
Nerve stimulation followed step by step
To prove the validity of this technique, the researchers visualized the diffusion in the brain of a nerve impulse generated by the electrical stimulation of the mustache of the rodent. The classic fMRI, which is slower, did not offer the possibility of determining the direction of circulation.
Limitations to overcome
Taking data requires complete immobility of the subject. Successive stimulations are essential to obtain a 3D image. The weakness of the signal could require the use of very intense magnetic field MRI, rare equipment. Next step: tests on awake humans.
Source: Toi et al., Science