Abstract
Purpose :
The mapping of visual input from the retina to neurons, called retinotopic mapping, has not been studied systematically in small animal models due to the insufficient spatial resolution of conventional neuroimaging techniques and the difficulty of precisely stimulating retinal locations. We developed an optical coherence tomography (OCT) system and a fundus camera stimulator and utilized for high spatiotemporal resolution retinotopic mapping of rat striate cortex.
Methods :
Anesthetized Sprague-Dawley rats were used for the study. A cranial window was implanted on the visual cortex for brain imaging. Throughout the experiment, physiological signals such as blood pressure, pCO2, and pO2 were maintained within the normal range. A fundus camera stimulator was designed to provide visual stimulus to a precise location on the rat retina. A custom built OCT angiography repeatedly acquired microvasculature of 1.5 mm 1.5 mm region of the visual cortex following the stimulus with a rate of a 3D angiogram per 0.7 second.
Results :
A flicker stimulus was applied to a circular region centered at optic nerve head (ONH) as shown in Figure 1(a). The contralateral visual cortex, shown in Figure 1(b), was imaged using optical intrinsic signal (OIS) imaging system to verify the center of the activation (Figure 1(c)). OCTA was performed to monitor hemodynamic response at a finer spatial scale. Dynamic changes of vessel diameters in the activated region were monitored using an OCT angiogram (Figure 1(d)). An increase in arterial diameter was observed as shown in Figure 1(e), which is a critical feature of neurovascular coupling. The regions where vessel diameters are measured indicated with colored boxes in the Figure 1(d). Red and orange color boxes represent arterial and arteriolar segments, respectively. OCT angiographic signals in multiple capillaries were increased due to the flow increase as shown in Figure 2. Capillaries that show more than 3% increase in the OCT angiographic signals are shaded in blue. This signal can be used as an indicator of stimulus-induced changes in neuronal activity.
Conclusions :
These results demonstrate the potential of the OCTA/fundus camera stimulator system for investigation of the retinotopic mapping in the small animal models. Investigation on precise retinotopic mapping upon highly localized visual stimulations will be presented.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.