Positron emission tomography study of the human hypothalamus during normal ageing and in ischemic and degenerative disorders.

During the period 1947-1959 twelve new-born mero-anencephalics were observed, who survived for more than 1 day after birth. Two even lived for 20 and 237 days, respectively. In 4 of the 12 children studied touching or slight pressure, and also faradic stimulation of various spots of the cerebro-vascular area were invariably followed by a facial expression which was very similar to smiling. Movies of it were shown to groups of impartial observers. In 78% the facial expression was judged to be a smile, a laugh or a grin. The neuroanatomical finding of a largely intact pontine tegmentum as being the most rostrally situated identifiable structure of the brainstem, has led to the hypothesis that the neural mechanisms underlying the smile are localized in the pontine tegmentum.