Feed-forward synchronization: propagation of temporal patterns along the retinothalamocortical pathway

Visual responses in the cortex and lateral geniculate nucleus (LGN) are often associated with synchronous oscillatory patterning. In this short review, we examine the possible relationships between subcortical and cortical synchronization mechanisms. Our results obtained from simultaneous multi-unit recordings show strong synchronization of oscillatory responses between retina, LGN and cortex, indicating that cortical neurons can be synchronized by oscillatory activity relayed through the LGN. This feed-forward synchronization mechanism operating in the 60 to 120 Hz frequency range was observed mostly for static stimuli. In response to moving stimuli, by contrast, cortical synchronization was independent of oscillatory inputs from the LGN, with oscillation frequency in the range of 30 to 60 Hz. The functional implications of synchronization of activity from parallel channels are discussed, in particular its significance for signal transmission and cortical integration processes.