Intrinsic signal imaging in macaque retina reveals different types of flash-induced light reflectance changes of different origins

Purpose. Intrinsic signal imaging is a newly developed technique that can map the neural activity of tissues noninvasively. It has been used to map the functional organization of the retina by recording flash-induced light reflectance changes in the cone and rod photoreceptors. The purpose of this study was to investigate the properties of the intrinsic signals in the monkey's retina, To accomplish this, the intrinsic signals and the electroretinograms (ERGs) evoked by the same stimuli were measured under different recording conditions. Methods. The fundus of macaque monkeys was observed with infrared light and recorded with a charge-coupled device (CCD) camera. The intrinsic signals were measured as retinal light reflectance changes induced by diffuse or focal flash stimuli. ERGS were recorded under the same stimulating conditions. The reflectance changes induced by different flash intensities, flash intervals, and background luminance were compared. Results. The intrinsic signals were categorized into different groups based on the location in the fundus. Fast signals (peak: similar to 100 ms) were recorded from the posterior retina including the fovea, and slow signals (peak: 5.0-6.0 seconds) were recorded from the optic disc and nonfoveal posterior retina. The threshold of the slow signal changes was comparable to that of the ERG b-wave, and the thresholds of the fast signals were higher than that of the ERG a- and b-waves. Conclusions. The retinal intrinsic signals are composed of several components with different response properties and different sources. This recording technique may be useful for mapping the retinal function in eyes with various disorders.