Abstract
We have developed an optical recording system to detect neural activity for a long time from 1020 sites of the cerebral cortex. But its signal-to-noise (S/N) ratio was insufficient for analyzing the neural response from single sweep recordings. Since there is no way to remove shot noise, to improve the S/N ratio for detecting the neural activity without averaging, we had to increase the excitation light intensity and enlarge signal size. For this purpose, we introduced a new illumination device using optic fiber bundle. Light from a halogen-tungsten lamp was rendered quasi-monochromatic by a band pass filter, converged to an optic fiber bundle and illuminated the preparation, which had been stained with a voltage-sensitive dye (RH414) in advance. A tandem lens system formed a magnified real image of the preparation, and the fluorescent light intensity was detected with a photodiode array. Neural responses to the electrical foot stimulation were monitored optically in the rat somatosensory cortex with this improved system. Among a large artifact derived from pulsation, we could detect neural response in a single sweep. Furthermore, with using digital subtraction, aligned at ECG, of a control record without stimulation, we succeeded in greatly reducing the pulsation artifact leaving the optical signal related to neural activity fairly intact. In this way, we could apparently detect cortical neural responses in vivo with a sufficient S/N ratio for analyses on the basis of single sweep recordings. [J Physiol Sci. 2006;56 Suppl:S185]
