LMI Seminar: Interferometric Imaging of Neural Signals
Prof. Daniel Palanker, Stanford University, CA
Nanometer-scale cellular deformations associated with changes of cell potential can reveal the underlying physiological activity. Using common-path quantitative phase microscope with a fast camera, we imaged cellular deformations of up to 3nm (0.9mrad) during the action potential in spiking HEK cells, and about 1nm in primary cortical neurons. The spike-triggered average movies reveal action potentials propagating across cells and along dendrites and axons, with time course matching the intracellular electrical recordings. Cellular deformations can be explained by dependence of the membrane tension on trans-membrane voltage.
Similarly, phase-resolved OCT can reveal changes in the shape of photoreceptors under light stimulus. Using a line-scan spectral domain OCT with adaptive optics, we observed that cone outer segments exhibit rapid axial contraction (7 – 40nm) after the stimulus, followed by a gradual swelling (50 – 400nm), which saturates within ~500ms. Latency of the rapid contraction and its scaling with the stimulus irradiance are consistent with the early receptor potential, associated with the charge movement across the outer segment disc membranes during photoisomerization.
Label-free optical monitoring of neural activity relates function to structure, and should greatly improve our functional imaging capabilities in neuroscience in general and in ophthalmology, in particular.