The functional impact of neurons in the dorsal lateral geniculate nucleus on the awake visual cortex

Date of Completion

January 2007


Biology, Neuroscience




Geniculocortical neurons provide a powerful synaptic drive to mammalian sensory neocortex. In vivo, this synaptic impact has generally been explored using cross-correlation analysis, which is usually limited to examining the influence of a single presynaptic neuron on a single postsynaptic target. Here, we combine spike triggered averaging and current source density analysis (Swadlow et al., 2002) to examine the monosynaptic currents generated in V1 by spontaneous impulses of single geniculocortical neurons of differing receptive field classes. Cortical recordings were obtained using a 16 channel silicone probe with 100-micron vertical spacing. The first study was designed to explore differences in the topography, amplitude, and time course of impacts generated from sustained and transient neurons of the LGN. In addition we examine the idea that differences in synaptic dynamics may partially mediate the sustained/transient response distinction We found that different geniculocortical axons generated distinct degrees of synaptic depression that were conserved over time and across their terminal arbors in layers 4 and 6. Surprisingly, however, synapses of Sustained neurons showed more, not less depression than those of Transient neurons. Nevertheless, Sustained neurons provided a strong and sustained flow of information to the cortex during maintained visual stimulation. These results show, for the first time, a clear relationship between synaptic dynamics and receptive field response dynamics of mammalian sensory neurons. ^