The origins of stimulus dependent intrinsic optical signals of the retina

Abstract

In order to determine the spatio-temporal properties and sources of functionally correlated intrinsic optical signals in the intact retina, we recorded intrinsic optical signals of the retina in vivo in the near-infrared (NIR, 700–900nm), while presenting a visible (550nm) stimulus. The stimulus set included counterflickering checkerboards and static patterns of various sizes, extents and contrasts. ERG/PERG recordings were also performed to provide an independent measure of retinal activity and optimal spatial frequency. Stimuli were presented in various portions of the retina and reveal that observe signals exhibited a non-uniform distribution across the retina.

In addition to the negative reflectance signal that mirrors cortical signals, there was often a strong positive (increase in reflectance) optical signal that was spatially offset to the region of the negative reflectance signal. The presence of this positive signal strongly depended on the retinal location of the stimulus such that the underlying source appears to have a superior-nasal bias. This positive signal was also strongly dependent on the focal plane of the imaging. This asymmetric spatial signal pattern, then, may reflect the architecture of the underlying circulation or deeper retina structures. Spatially asymmetric patterns in one eye were, not surprisingly, found to be distributed in mirrored fashion in the other eye. Static stimulus patterns as well as counterflickering stimuli elicited strong responses. Action spectra of these signals were measured and related to expected hemoglobin sources.

Footnotes

 Supported by NIH EY12915, EB002843 and the Glaucoma Research Foundation.