Clinical case Hand up! Yawn and raise your arm

Background In some cases of hemiplegia, the initiation of yawning is associated with involuntary raising of the paralysed arm. Reports are scarce in the literature, probably because the phenomenon has largely been overlooked. Methods We studied six patients from two neurologic units, and compared them with published cases from the last 200 years. Brain imaging typically shows a small vascular lesion most often located in the internal capsule. Results After comparison with experimental models in cats, we suggest that damage to the cortico-neocerebellar tract of the extrapyramidal system disinhibits the spino-archeocerebellar tract, enabling a motor stimulation of the arm by the lateral reticular nucleus, which harmonises both central respiratory and locomotor rhythms. Conclusions When phylogenetically primitive structures are disinhibited, they regain autonomy in the homeostatic process associating the massive inspiration of yawning – a form of behaviour that stimulates vigilance – with a motor control mechanism that is active during locomotion. For this phenomenon, we coined the term ‘parakinesia brachialis oscitans’.