The avian red nucleus: a comparative physiological and behavioural study on Columba livia

An anatomical and morphological study of the red nuoleus of the pigeon showed that as in the mammal the nucleus is relatively highly vascularised and contains both large and small cells. The only relevant previous source indicated the existence of large cells only. Lesions of the pigeon red nucleus (r. n.) effected a variety of symptoms including torticollis, abnormalities of leg muscle tone and movement, hyporeactivity, aphagia and asymmetry of pupil dilation although the latter was probably due to third nerve damage. Electrical stimulation of the r. n. produced contralateral circling and indications of staxia. Extensive investigation using electrical stimulation and evoked potential recording revealed telencephalic inputs to the r. n. from the archiastriatum medialis, hyperstriatum ventrale, parolfactory lobe, olfactory bulb and neostriatum intermedium, diencephalic projections from the lateral hypothalamus and nucleus rotundus and a cerebellar link with the nucleus lateralis. Comparison tdth mammalian connections disclosed some similarities and in addition suggested that links with amygdala and septum may exist in the mammal. Evoked potential and single unit recordings following visual, somaesthetic and auditory stimulation demonstrated that the avian r. n. and individual cells respond in a very similar manner to that of the mammal. An olfactory projection was also demonstrated by nerve stimulation. Investigation of the effects of r. n. lesions on previously established avoidance behaviour disclosed complete disruption of learning. Similar effects were shown on a pattern discrimination acquired under positive reinforcement, although brightness aid colour discriminations were not affected. Possible mechanisms involving the r. n. in behaviour control are discussed.