Abstract
The common ancestor of Pan and Homo, lived in tropical forests about eight million years ago, and its population was divided into two, western and eastern, by the Rift valley that crosses the equator from north to south in eastern Africa. The former group thrived in the forest and became chimpanzees, whereas the latterevolved on the savanna to become humans (Coppens, 1994).
Understanding the role of mastication in the phylogeny of humans is very important for understandingthe genesis of the marked encephalization of the human cortex.
The interaction between mastication of chewing gum and cerebral blood flow (CBF) was studied in twelve healthy volunteers aged 18 to 40 years. Positron-emission tomography (PET)-autoradiography was carried out after bolus injection of 1.5 GBq H215O (oxygen-15-labelled water), which has a half life of 2 min. The PET images were superimposed on magnetic resonance (MR) images of each subject.The regional cerebralblood flow (rCBF) images were normalized by the global CBF value, and subtraction images (those obtained during gum-chewing minus those during resting) were created and recut at the MR image slice positions. Gum specially designed for chewing training was used.
