Image: LANA FINCH/Courtesy of the Proceedings of the National Academy of Sciences
It's not going to win any beauty contests, but the naked mole-rat does have the distinction of being one of the most unusual mammals around. Not only does the creature differ from its furred kin in having a so-called eusocial colony structure composed of multiple workers and a single breeding female, or queen (much as bees and other social insects do), it also exhibits a number of distinguishing anatomical traits. Indeed, bare-skinned (save for a sprinkling of sensory hairs), wrinkled, and small of eye and ear, the naked mole-rat stands alone. Researchers have long recognized that a number of these characteristics are adaptations to the naked mole-rats underground habitat. Oddly enough, the most important of these adaptations is the rodents greatly enlarged incisor teeth, the lower two of which can actually move independently of one another to aid in digging and manipulating objects, among other things. Now new research suggests that parts of the beast's brain have undergone similarly striking specialization. The findings appear in the current edition of the Proceedings of the National Academy of Sciences.
Using microelectrodes to record neuronal activity in the rodents, Kenneth C. Catania and Michael S. Remple of Vanderbilt University determined that nearly one third of the naked mole-rat's so-called primary somatosensory cortex (the part of the brain related to touch) is devoted to sending and receiving information to and from those bizarre front teeth. The animal's forepaws, in contrast, are allotted only 10 percent of cortex space. (The image at the right shows the relative proportions of body parts as they are represented in the naked mole-rat's neocortex.) Furthermore, the team found, the mole-rat somatosensory cortex is significantly larger relative to the size of the entire neocortex than that of closely related lab rats.
Catania and Remple also report that the naked mole-rat's somatosensory cortex appears to have taken over all areas of the neocortex normally devoted to vision. For now, the payoff of devoting so much of the cortex to the teeth remains unclear, the authors note. But whatever the reason, these new results, they assert, "indicate that major cortical remodeling has occurred in naked mole-rats, paralleling the anatomical and behavioral specializations related to fossorial life."
ABOUT THE AUTHOR(S)
Kate Wong is a senior editor for evolution and ecology at Scientific American.