Cortical control of claw cutting in the rat

Claw cutting emerges as a behavior between Postnatal Day 30 and 50, and by Day 100 at least 80% of rats have cut their claws. Complete frontal ablation or total decortication at any age abolished claw cutting, but complete posterior neocortex removal did not. In adult rats, motor cortex ablations or hemidecortications abolished claw cutting, whereas the same lesions given to infant rats spared claw cutting. Neonatal telencephalic noradrenaline depletion had no effect on the development or incident of claw cutting. Loss of claw cutting appears to be due to loss of efficient biting and chewing rather than to an inability to orient or to groom. The sparing after infant ablations may be due to functional reorganization of tissue within, or adjacent to, the developing motor cortex. The study demonstrates that careful examination of features of the laboratory rat's appearance can provide useful clues about its behavioral competencies. Furthermore, abnormalities such as loss of claw cutting can serve as a useful diagnostic indication of specific kinds of brain damage.