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 (r = 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.

The Cavalieri method and the optical fractionator were employed to estimate the volume and neuron numbers, respectively, of the dorsal lateral geniculate nucleus (dLGN) in seven adult male pigtail monkeys (Macaca nemestrina). Unbiased estimates were selectively obtained for the parvocellular (P), magnocellular (M), and interlaminar plus superficial (I + S) layers of the nucleus. The dLGN had a mean volume of 56.5 mm3, and contained on average 1.79 million neurons. The P layers contributed 64% of the volume and 83% of the neurons in the dLGN; the corresponding proportions for the other layers were 13% and 9% (M), and 23% and 8% (I + S). Interindividual variability was large for neuron counts, which varied within a two-fold range, and lower for volume estimates. Since no published data are available for the pigtail dLGN, the present results are compared with quantitative studies of the dLGN in other macaque species, placing special emphasis in the discussion of the methodologies used.