Synchronous oscillations in the cortex, LGN and retina of the cat: how are they related?

Synchronous oscillations within a broad range of frequencies have been described for visual responses in retinal ganglion cells which are transmitted by the lateral geniculate nucleus (LGN), raising the question of how oscillatory inputs contribute to synchronous oscillatory responses in the cortex. We have made simultaneous recordings from visual areas 17 and 18 as well as the LGN and retina of the anaesthetized cat to examine how the occurrence of synchronization in the cortex follows subcortical oscillatory responses. Strong correlation of oscillatory responses was observed between the retina, LGN and the cortex. This finding provides evidence that cortical neurons may follow retinal oscillatory responses relayed by the LGN. In many cases, however, the development of cortical synchronization was independent of the temporal structure of the incoming inputs, excluding a simple feedforward mechanism for cortical synchronization. It is possible that depending on the stimulus, synchronous input from the LGN could facilitate synchronization of cortical responses by intracortical mechanisms and thereby contribute to the binding of features of objects.