Real-time imaging of action potentials in nerves using changes in birefringence

Polarized light can be used to measure the electrical activity associated with action potential propagation in nerves, as manifested in simultaneous dynamic changes in their intrinsic optical birefringence. These signals may serve as a tool for minimally invasive neuroimaging in various types of neuroscience research, including the study of neuronal activation patterns with high spatiotemporal resolution. A fast linear photodiode array was used to image propagating action potentials in an excised portion of the lobster walking leg nerve. We show that the crossed-polarized signal (XPS) can be reliably imaged over a ≥2 cm span in our custom nerve chamber, by averaging multiple-stimulation signals, and also in single-scan real-time "movies". This demonstration paves the way toward utilizing changes in the optical birefringence to image more complex neuronal activity in nerve fibers and other organized neuronal tissue.