Figure 6.

(A) Neuron numbers (in supragranular and infragranular layers) per mm² of cortical surface area in the rostral and caudal poles of the isocortex. Species are ordered by total number of isocortical neurons. Species with more isocortical neurons exhibit a greater range of variation in neuron numbers under 1 mm² of cortical surface between the rostral and caudal poles. The range of variation in infragranular layer neurons is relatively small in primates and in rodents. The error bars indicate the standard errors for the respective layers (not for the total number of neurons in the column) (B) Density of neurons at the rostral and caudal poles in supra- (plotted on top) and infragranular layers (plotted at bottom). The range of variation in neuron numbers is similar to the range of variation in neuron density between the rostral and caudal poles across species. (C) A visualization of the implied height of the cortical columns, within the layers of which the stipple density is proportional to neuronal density, shows a rostro-caudal decrease in column height.