Tag Archives: Posterior cranial fossa

Cerebellum and paleoneurology

cerebellaCerebellum is the Latin word for “little brain”. As a portion of the brain, the cerebellum is part of the Central Nervous System. It is located below the occipital and the temporal lobes of the cerebral cortex, housed within the posterior cranial fossa.

Anatomy and functions

The cerebellum is composed by four cerebellar deep nuclei surrounded by the cerebellar cortex. It is separated by the cerebral hemispheres through the tentorium cerebelli, and the two cerebellar hemispheres are separated by the falx cerebelli. All these connective meningeal layers are anchored orthogonally to the main ridges of the posterior fossa, namely those associated with the venous sinuses and the temporal pyramids. The three divisions of the cerebellar cortex correspond to three functional and phylogenetic subdivisions. The flocculonodular lobe (the ancient part of the cerebellum) regulates balance and reflexes, such as eye movement; the vermis has a role in motor coordination (body movements); and the lateral hemispheres are implicated in planning complex movements and in cognitive functions, in concert with the cerebral cortex. One fundamental human characteristic, language, has been shown to require both sensorimotor and cognitive functions of the cerebellum, because of the motor control associated with the vocal apparatus and the perception and performance of speech (Mariën et al., 2012). The cerebellum has been suggested to play a role in autism.

Evolution

The spatial position of the cerebellum is different among the human species. In modern humans it is positioned under the temporal areas, in Homo erectus almost under the occipital lobes, and in Neanderthals under the parietals (see Bruner, 2003). The cerebellar structures co-evolved (physically and functionally) together with the cerebral cortical areas (Whiting and Barton, 2003; Balsters et al., 2009), as well as with other brain structures, such as the brainstem (Baizer, 2014). Anne Weaver (2005) proposed that the cerebellum underwent a volumetric increase in Neanderthals and anatomically modern humans. Because of a relevant association between cognitive and technological demands, Barton (2012) supports a “sensory-motor origin of socio-cognitive capacities”, stressing the value of the cerebellar functions in the evolution of the human brain. Given this renewed attention toward the cerebellar areas and the limited data available on their functions and levels of organization, paleoneurological analyses can supply relevant information on its patterns of evolution within the human genus.

Recently, in a book dedicated to Neanderthals and modern humans, Daisuke Kubo and coworkers developed a method for estimating cerebellar volume from magnetic resonance data.  First by comparing metrics from the posterior cranial fossa obtained from MRI or computed tomography (CT) from the same subjects they determined that the method was reliable. Then, they extracted both cerebellar and posterior cranial fossa regions from MR images to evaluate the correlation between cerebellar volume and diameters of the posterior endocranial fossa. Their results show that the correlation is pretty high, and measurements taken from endocasts can therefore be used to provide reliable estimations of the cerebellar volume. So good news for paleoneurologists, who can use endocranial landmarks to provide useful information on cerebellar differences among fossil hominids.

Ana Sofia Pedro

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