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A.J. Valjakka; The Reflection of Retinal Light Responses Onto the Superior Colliculus and the Visual Cortex in Rats . Invest. Ophthalmol. Vis. Sci. 2005;46(13):5672.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The characteristics of functional associations of light stimulus–evoked responses between the retina and the superior colliculus (SC) & the primary visual cortex (VC) were investigated, in rats. If systematic associations of responses between the retina and later visual steps could be demonstrated, the condition of parts of the retina, such as ganglion cells and the optic nerve, which themselves do not contribute notably to the polarization phenotype of ERG response, could also be evaluated. Methods: The field potential responses to a range of flash intensities were recorded simultaneously from the temporal scleral site of the eye and from the optic layer of the contralateral SC & the skull site over the VC. The records were acquired from the non–restrained & –drugged albino (Sprague–Dawley) rats, during the alert immobile behavioral stage, by applying an electrode detector and a visual stimulator designed for this purpose and which provided comparable records to those obtained from anesthetized animals. Results: In all the cases, the sizes (& latencies) of different phases of field potential responses of the retina (a– & b–wave), SC (peak–1 & –2) and VC (peak–'1') showed two successive saturation steps with increasing stimulus intensity, but the forms of the associated functions differed from each other substantially. Additionally, the rate of decrease of response latencies by increases in flash intensity were found to be greatest in the retina, intermediate in the SC and smallest in the VC. However, the grade of polarization degree of the retinal a–wave trough was consistently but in a skewed way copied by the consequent polarization response of the SC, and the non–linear asscociation applied between the SC and the VC as well. Accordingly, the light response functions of the retina–vs.–SC and the SC–vs.–VC structures were the systemically skewed mirror images of each other which respectively involved the non–linear logarithmic/near square root–scale transformation of responses sizes, but over the adaptively varying range of response amplitudes. Conclusions: The data show that the coding of light stimulus intensity by the field potential polarization responses of the SC and VC correlates in a non–static and an adaptive way to the ERG's a–wave polarization response of the retina, in rats. Because this relationship is fully adaptive in character, with respect to timing and size of associated responses, it cannot be identified by mere inspection of single response pairs of any type. The demonstrated relationship can applied for evaluating the condition of the ganglion cells and the optic nerve as a whole.
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