All Rodents Are Not the Same: A Modern Synthesis of Cortical Organization

Abstract

Rodents are a major order of mammals that is highly diverse in distribution and lifestyle. Five suborders, 34 families, and 2,277 species within this order occupy a number of different niches and vary along several lifestyle dimensions such as diel pattern (diurnal vs. nocturnal), terrain niche, and diet. For example, the terrain niche of rodents includes arboreal, aerial, terrestrial, semi-aquatic, burrowing, and rock dwelling. Not surprisingly, the behaviors associated with particular lifestyles are also highly variable and thus the neocortex, which generates these behaviors, has undergone corresponding alterations across species. Studies of cortical organization in species that vary along several dimensions such as terrain niche, diel pattern, and rearing conditions demonstrate that the size and number of cortical fields can be highly variable within this order. The internal organization of a cortical field also reflects lifestyle differences between species and exaggerates behaviorally relevant effectors such as vibrissae, teeth, or lips. Finally, at a cellular level, neuronal number and density varies for the same cortical field in different species and is even different for the same species reared in different conditions (laboratory vs. wild-caught). These very large differences across and within rodent species indicate that there is no generic rodent model. Rather, there are rodent models suited for specific questions regarding the development, function, and evolution of the neocortex.

Evolution of centralized nervous systems: Two schools of evolutionary thought

“…Hennig (53) also discovered that character polarity (i.e., primitive or derived) could be determined by an outgroup rule, which proposes that, when two or more homologous characters occur within a group, the character outside the group is the primitive character, whereas the character found only within the group is the derived character. Realization of the predictive power of the outgroup rule in the work by Hennig (53) has given rise to a wide range of evolutionary studies that have attempted to reconstruct the phylogenetic history of molecular characters (58), morphological characters (59-61), behavioral and ecological characters (62), and biogeographical events (63). Such studies are usually called cladistic studies, because they rely on the outgroup rule in the work by Hennig (53), although they deal with the phylogeny of a character rather than reconstructing the phylogenetic history of taxa.…”

Sensory evolution in blind cavefish is driven by early embryonic events during gastrulation and neurulation

“…To cite a few examples, diurnal rodents have a larger proportion of cerebral cortex devoted to visual areas than nocturnal rodents, the latter having a larger part of their cortex devoted to somatosensory and auditory areas (Campi and Krubitzer, 2010;Krubitzer et al, 2011). Among cichlid fish in African lakes, the relative size of brain regions in different species varies according to the environment and feeding habits (Pollen et al, 2007).…”

Conceptual and methodological issues in comparative neuroscience and psychology: a reassessment

“…For example, raccoons possess a particularly large (larger than the cortical hand area in humans) cortical representation of their forepaws (Welker and Seidenstein 1959). Also, species of rodents differ widely in their cortical organization, and these differences can be linked with lifestyle and ecological variables (Krubitzer, Campi, and Cooke 2011).…”