Figure 2.

Scaling of the neocortex in different mammals. Comparative studies demonstrate that the neocortex scales linearly or non-linearly. Capybaras can weigh up to 91 kg and have an enlarged brain and neocortex compared to the closely related guinea pig, which weighs 700 g. The more distantly related California ground squirrel has a similar body size to that of the guinea pig, but the scaling of the cortical sheet and cortical fields compared to the capybara is non-linear, and there is an increase in the number of cortical fields. An extreme example of a non-linear increase in the size of the cortical sheet is observed in squirrel monkeys. Although squirrel monkeys are of a similar weight (750 g) compared to the guinea pig and California ground squirrel, they have a relatively large neocortex (about the size of the capybara's), a relative decrease in the size of primary cortical fields (e.g., A1, S1, V1) as a percentage of overall cortical area, and the addition of cortical fields (note that not all known cortical fields in the squirrel monkey neocortex are shown; the blank areas contain additional cortical fields). All brains are drawn to scale. The work on the guinea pig and capybara is modified from Campos and Welker (1976); the divisions of the ground squirrel are redrawn from Krubitzer et al. (2011); divisions of the squirrel monkey are redrawn from Kaas (2012). Other conventions as in previous figure.