Numerical relationship between neurons in the lateral geniculate nucleus and primary visual cortex in macaque monkeys.

We examined the numerical correlation between total populations of neurons in the lateral geniculate nucleus (LGN) and the primary visual cortex (area 17 of Brodmann) in ten cerebral hemispheres of five normal rhesus monkeys using an unbiased three-dimensional counting method. There were 1.4 +/- 0.2 million and 341 +/- 54 million neurons in the LGN and area 17, respectively. In each animal, a larger LGN on one side was in register with a larger area 17 of the cortex on the same side. Furthermore, asymmetry in the number of neurons in both the LGN and area 17 favored the right side. However, because of small variations across subjects, correlation between the total neuron number in LGN and area 17 was weak (r2 = 0.29). These results suggest that the final numbers of neurons in these visual centers may be established independently or by multiple factors controlling elimination of initially overproduced neurons.