Abstract
Multiple-site optical recording of neural activity provides a powerful tool for the cerebral cortical neurophysiology. However, to detect the membrane potential optically from the intact cortex, reflected-light fluorescence method must be used and the optical signal usually has low signal-to-noise (S/N) ratio and requires summation. Therefore, the application of the optical recording of the membrane potential to the cortex has been restricted to reproducible, stimulus-evoked activation. We have developed an optical recording system suitable for detecting on-going cortical activity, with high S/N ratio enough for single-sweep analysis, by using fiber optics as the excitation light source, and applied this system to the intact rat cortex. The sensorimotor region was exposed and stained with a voltage sensitive dye (RH414) without peeling dura. The electroencephalogram (EEG) was recorded simultaneously with an electrode placed in the optical monitoring area. Deflections time-locked to large, irregular EEG activities emerged in the optical recording after the pulsation artifacts were largely reduced by software. The optical signal was distributed over a broad region, whose time course, amplitude or shape varied within the region with slight differences in the onset time. This possibly reflected regional differences of the neural activities in the cortex which produced the EEG transient. Thus, our system could be a powerful tool to study spatial organization of spontaneous cortical activities. [J Physiol Sci. 2007;57 Suppl:S109]
