Membrane Potential Microscope for Functional Brain Imaging

Abstract

We have developed a membrane potential microscope for monitoring neural activity in the cortex stained with a voltage-sensitive dye. The microscope captures images using a high-speed camera, and its optical apparatus is designed for experiments on small primates (monkeys). The camera uses a custom-made CCD chip that has 1776H × 1626V pixels and 16 parallel output terminals. By incorporating the pixel-binning technique, the camera produced 296H × 271V pixel-images at a rate of approximately 2.5 ms/frame. The acquired images were then processed to produce functional brain images of somewhat reduced resolutions (the resolution reduction being as a consequence of spatio-temporal filtering). Special lenses for the optical apparatus gave a nearly uniform illumination over the wide CCD active area of 20.4 × 18.7 mm. Tests of the microscope showed that it could visualize neural activity in the somatosensory cortex of macaque monkeys (Macaca fuscata).