Paper short abstract:

We estimated the cerebellar-cerebrum volume ratio of Middle Paleolithic modern humans and Neanderthals. The former is comparable to the present-day humans, while the Neanderthals have had relatively small cerebella. Co-authors: Tanabe H, Ogihara N, Yogi A, Murayama S and Ishida H.

Paper long abstract:

Neanderthals are an extinct human species who had large brains comparable to modern humans. To what extent Neanderthal cognitive abilities were similar to those of modern humans is currently under intensive debate. We compared the cerebro-cerebellar volume ratio as a plausible way to infer the difference in cognitive ability among the Neanderthals, Middle Paleolithic modern humans, and present-day humans.

First, we devised a new method to estimate the cerebral and cerebellar volumes, which was derived from the volumetric relationships between endocranial subregions (i.e. supratentorial and posterior cranial fossa regions) and brain components (i.e. cerebrum and cerebellum) based on MRI data of living human subjects (n=32). To validate the accuracy of MRI measurements, the volumes of endocranial portions were calibrated by coefficient factors derived from paired comparison between the CT and MRI measurements of the same individuals (n=3). We found that the volumes of endocranial subregions are useful estimators for the cerebral/cerebellar volumes.

We then applied our estimation method to the Neanderthal (n=3) and the Middle Paleolithic modern humans from Levant (n=2). The results were partly consistent with previous reports that the Neanderthals have relatively smaller cerebella compared to the living human sample. On the other hand, we also found that the earlier Levantine specimens are comparable to the living human sample in their relative cerebellar volumes. These results indicate that the Middle Paleolithic modern humans already have had cognitive functions comparable to present-day humans while the Neanderthals have not.