Functional Imaging

During the past decade in brain research, optical techniques have assumed a prominent role in addressing physiological and biochemical questions on cellular and sub-cellular levels. One of the primary reasons for the advent of optical imaging in Neuroscience has been the widespread acceptance of confocal microscopy and multiphoton microscopy, both of which make it possible to image from within light-scattering preparations, such as living brain tissue (see topic on Structural Imaging). Using the ever-increasing array of fluorescent indicators, including both molecular and genetically encoded probes, researchers have been able to probe such important physiological parameters as the concentrations of various intracellular ions and membrane potential. Using these techniques, it has been possible to collect, in addition to high-quality structural images, high-fidelity functional signals from brain slices and even intact cortex.

We have used both widefield and scanning microscopy for functional imaging of neuron populations and individual nerve cells. Utilized widefield systems include photodiode arrays and CCD cameras, while scanning approaches used non-confocal random-access laser scanners, confocal and multi-photon microscopes. Employed optical indicators were fluorescent voltage-sensitive dyes for imaging levels transients of membrane potential, as well as ion-indicators such as calcium-sensitive dyes to image levels and fluxes intracellular ions. On a related note, we have recently measured calcium transients in individual dendritic spines with confocal microscopy and multi-photon microscopy.