Optical recording of fast neuron activities

Spatiotemporal imaging of neuronal activity in the brain plays a critical role in studies of brain function and disorders. However, thorough monitoring of neuronal activity in the brain has been far from practical due to the limitations of conventional technologies. Since brain activity is fundamentally the ensemble of excitation of neuronal cells, it exhibits extremely high spatiotemporal heterogeneity on the micrometer and millisecond scale. Further, a number of functional studies are accompanied by behavioral control and/or observation. An ideal functional imaging technology, therefore, would involve noninvasive, label-free and three-dimensional dynamic imaging of cortical neuronal activity with µm and ms resolution. Optical methods look like one of the most feasible approaches because fast optical signals of neuronal activity have several advantages over conventional methods, including the advantages that they require no probe and thus can be recorded noninvasively in 3D. It is logical to start from validating the measurement of fast optical signals in the fundamental unit of the neural system (neurons) and then pursue toward the measurement in the most complex neural system (human brain). As several scientists had reported the measurement of fast optical signals in large neurons isolated from low-level animals, we performed the next step in this study - optical measurement of neuronal activity in ex vivo brain tissue.