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A. J. Valjakka, J. Ahonen; Discrete Moments of the Brain Responsiveness in Describing the Given Information Coming From the Retina. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1078.
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To compare the response generations in the retina vs. superior colliculus (SC) over the two time points of response deflections of the SC. Retinal electroretinogram (ERG) and SC visual evoked potential (VEP) responses to light stimulation were recorded from the freely behaving rats, using a visual stimulator and a specific eye electrode.
The ball electrodes (1.2-mm-diameter silver ball with a flexible Teflon-coated lead) were implanted against the sclera of the eyes, and the thread electrodes were implanted within the optic layer of the SC, in Wistar rats, under anaesthesia. Half of the rats underwent a two week light exposure, the other half serving as the unexposed controls. Rats were stimulated with white flashes of different intensities under constant background illumination.
Retinal ERG b-wave response component amplitudes correlated with both the SC peak-1 and peak-2 response component amplitudes, while peak-1 and peak-2 appeared successively and had opposite polarities. This correlative result was true for both the controls and light exposed rats, even though the latter had retinal photoreceptor degenerations, reduced responsiveness and changes in forms of related light response functions. In contrary to above the retinal ERG a-wave response component moment correlated only with the peak-1 moment, but not with the latency of the subsequent peak-2, of the SC. Here too this correlative result was true for both the controls and light exposed rats.
These data suggest that the modulation of discrete moments of a given system state, and obviously points of associated impulse responses, of the SC, are the relevant variables in describing the information properties coming from the retina. The delay between the peak-1 and peak-2 highlights the obvious non-stable/collapsing state of the SC neuron network that might be a prerequisite for the readiness of the succeeding encoding of the accessory information that would subsequently be delivered from the retina.
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