For example, in the cat, the three main physiological classes of thalamic neurons (X, Y, W) reflect responses that correspond to X, Y and W cells in the retina ( Sherman and Spear, 1982). Moreover each functional class of TC seems to be driven by a corresponding functional class of RGC. Consistent with low convergence, receptive field properties of TCs and RGCs are similar ( Grubb and Thompson, 2003). First, several studies argue that only a few RGCs innervate each TC ( Cleland, 1971 Hamos et al., 1987 Mastronarde, 1992 Usrey et al., 1999 Chen and Regehr, 2000 Hong et al., 2014). Previous evidence suggested that the LGN network might be relatively easy to understand. We used this approach to describe what we expected to be one of the most straightforward CNS pathways: the connections between retinal ganglion cells and thalamic neurons projecting to cerebral cortex.
By exploring collateral branches of these same axons one can also learn how axons distribute their innervation among all the postsynaptic cells in a region of the brain.
FUZZYTIME JUNKTION SERIAL
Because the heavy metal stains used for electron contrast label all cell membranes, circuit tracing in serial electron microscopy reveals the actual cohorts of presynaptic axons that connect to a postsynaptic cell. Serial section electron microscopy provides access to the full patterns of synaptic connections linking nerve cells together.
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