Transcranial sonography: a technique for the study of the temporal lobes of the human and non-human primate brain.

We developed a modified transcranial sonography technique to study the morphology of the temporal lobe, a brain region involved in language, memory and social functions in humans that can be visualized in correspondence of the acoustic window of the temporal squama. Previous studies raise the possibility that a unique derived feature of Homo sapiens is a relatively larger temporal lobe compared to those of other hominins and apes. Such a brain reorganization might have contributed to the evolution of various "higher" cognitive functions of Homo sapiens, including language. Hence, the importance of further comparative analyses of the temporal region. With the technique that we developed we were able to study the meninges, the subarachnoidal space and the cortex of the human temporal lobe. The spatial resolution and the ability to visualize structures of 200-300 microm size led us to hypothesize that the linear structures parallel to the subarachnoidal space might be referred to the neuronal layers of the cortex. The low cost, simplicity and safety of the procedure suggest that this technique may have a significant potential in the comparative study of the primate temporal lobe. Furthermore, the procedure described here can also be used for the study of vascularization of the meninges, in order to better understand the evolutionary relationships between the neurocranial shape and the middle meningeal vessels in living and fossil human species.