Sensorimotor aspects of flight control in birds: specializations in the spinal cord.

Avian bipedal locomotion and flight suggest specializations in sensorimotor integration as compared to quadrupedal vertebrates. Specializations at the level of the spinal cord were studied with neuroanatomical tracing experiments in pigeons. Bird-specific connections were found in the exteroreceptive system (receptors associated with feathers) and in the proprioreceptive system (spinocerebellar pathways). These specializations seem to be related to flight control. Neurons of the marginal nuclei (accessory lobes) in the lumbosacral cord, which are unique to birds, have propriospinal connections mainly to the contralateral ventral cord. The functional role of these nuclei remains enigmatic.