Abstract
Purpose: :
To characterize the properties and interrelations of field potential response (FPR) inductions over the different layers of the superior colliculus (SC) in the rat in association with different flux changes in the retina–stimulating light.
Methods: :
Albino Wistar rats (n=9) were permanently implanted with an array of four electrodes positioned at the superficial gray , optic, intermediate gray and deep gray layers of the SC. Related FPRs were recorded to flashes of different relative fluxes covering a range of 5 log–units from the mesopic to scotopic level. Free–field flashes, stimulating uniformly the whole retina, were delivered when the rats, not treated by any drugs, showed spontaneously the alert immobile behavioral stage.
Results: :
FPRs of basically identical form and at near synchronized times were evoked across the SC. However, the modulation of response amplitudes with flashes showed four mutually distinctive features when inspected over different SC layers. The sigmoid response amplitude–intensity function was progressively damped in appearance, with an increase and decrease in, correspondingly, the lower and higher saturation levels, while shifting from superficial to deeper layers of the SC. However, the 'sigmoid' signal–to–noise ratio–intensity functions showed relatively consistent appearance over the different SC layers, except for a conspicuous rise in the lower plateau level for the deeper SC layers. The latter resulted in a marked response contrast between the superficial vs. deep layers of the SC with the smallest stimulus intensities, the difference in which progressively diminished when flash intensity was increased. The mutual synchrony of different frequency components of the FPRs over the different SC layers rose steeply with increases in flash intensity, without saturation. The signal–to–noise ratio of the difference in signals, those first subjected to discrete derivation, also rose without saturation, in the ‘first response phase’, and was practically constant in the ‘second response phase’ over the flash intensity range tested.
Conclusions: :
The data suggest that the coding of flux change in light in the dendritically interconnected neural network of the SC, which is functionally directly relatable to the retinal sensation of light in the first phases of the SC response, have many functional expressions which are based on the relative degrees of synchrony and de–synchrony of the SC neural network.
Keywords: superior colliculus/optic tectum • electrophysiology: non-clinical • brightness and lightness