On the functional role of gamma synchronization in the retinogeniculate system of the cat

Abstract

Fast gamma oscillations, generated within the retina, and transmitted to the cortex via the lateral geniculate nucleus (LGN), are thought to carry information about stimulus size and continuity. This hypothesis relies mainly on studies carried out under anesthesia and the extent to which it holds under more naturalistic conditions remains unclear. Using multi-electrode recordings of spiking activity in the retina and the LGN of the cat, we show that visually driven gamma oscillations are absent for awake states and are highly dependent on halothane (or isoflurane). Under ketamine, responses were non-oscillatory, as in the awake condition. Response entrainment to the monitor refresh was commonly observed up to 120 Hz and was superseded by the gamma oscillatory responses induced by halothane. Given that retinal gamma oscillations are contingent upon halothane anesthesia and absent in the awake cat, such oscillations should be considered artifactual, thus playing no functional role in vision.