Researchers have discovered a sophisticated neural computer, buried deep in the cerebellum, that performs inertial navigation calculations to figure out a person’s movement through space.

These calculations are no mean feat, emphasized the researchers. The vestibular system in the inner ear provides the primary source of input to the brain about the body’s movement and orientation in space. However, the vestibular sensors in the inner ear yield information about head position only. Also, the vestibular system’s detection of head acceleration cannot distinguish between the effect of movement and that of gravitational force.

Angelaki and colleagues based their brain studies on the predictions of a theoretical mathematical model postulating that the brain could compute inertial motion by combining rotational signals from the semicircular canal in the inner ear with gravity signals.

They concentrated their search for the brain’s inertial navigation system on particular types of neurons, called Purkinje cells, in a region of the cerebellum known to receive signals from the vestibular system. This region is known as the posterior cerebellar vermis, a narrow, worm-like structure between the brain’s hemispheres.

In their experiments, the researchers measured the electrical activity of these Purkinje cells in monkeys as the animals’ heads were maneuvered through a precise series of rotations and accelerations. After analyzing the electrical signals measured from the Purkinje cells during these movements, the researchers concluded that the specialized Purkinje cells were, indeed, computing earth-referenced motion from head-centered vestibular information.

The researchers concluded that the output of the Purkinje cells indicates an “elegant solution” to the computational problems involved in inertial navigation.

The researchers include Tatyana A. Yakusheva, Aasef G. Shaikh, Andrea M. Green, Pablo M. Blazquez, J. David Dickman, and Dora E. Angelaki of Washington University School of Medicine in St. Louis, MO.

“Purkinje Cells in Posterior Cerebellar Vermis Encode Motion in an Inertial Reference Frame.” Yakusheva et al.: Neuron 54, 973–985, June 21, 2007. DOI 10.1016/j.neuron.2007.06.003

For nearly a century, anthropologists have been debating the relationship of Neanderthals to modern humans. Central to the debate is whether Neanderthals contributed directly or indirectly to the ancestry of the early modern humans that succeeded them.

As this discussion has intensified in the past decades, it has become the central research focus of Erik Trinkaus, Ph.D., professor of anthropology at Washington University in St. Louis. Trinkaus has examined the earliest modern humans in Europe, including specimens in Romania, Czech Republic and France. Those specimens, in Trinkaus’ opinion, have shown obvious Neanderthal ancestry.

In an article appearing the week of April 23 in the Proceedings of the National Academy of Sciences, Trinkaus has brought together the available data, which shows that early modern humans did exhibit evidence of Neanderthal traits.

“When you look at all of the well dated and diagnostic early modern European fossils, there is a persistent presence of anatomical features that were present among the Neanderthals but absent from the earlier African modern humans,” Trinkaus said. “Early modern Europeans reflect both their predominant African early modern human ancestry and a substantial degree of admixture between those early modern humans and the indigenous Neanderthals.”

This analysis, along with a number of considerations of human genetics, argues that the fate of the Neanderthals was to be absorbed into modern human groups. Just as importantly, it also says that the behavioral difference between the groups were small. They saw each other as social equals.

Source: Washington University in St. Louis.