What Makes Us Human?

Sunday, August 5, 2012

What makes us human? Aside from the longer lower limbs, opposing strong thumb, and the position of the foramen magnum at the center of the base of the skull, there are two other features, located in the central nervous system, which make us act differently from apes (chimps and gorillas). These are two myelinated fiber bundles, called fasciculus (pl fasciculi), linking different areas of the cerebral cortex; the arcuate fasciculus and the uncinate fasciculus. They are what makes us unique among primates.

The arcuate fasciculus is the bundle of nerve cell fibers which extends from the Wernicke area, in the top back region of the temporal lobe, to the Broca area in the frontal lobe, forming an arch inside the left cerebral hemisphere. The Wernicke and Broca areas are the two centers of language in the human brain: the first is the language understanding center that enables us to understand what is being said, from a semantic and syntactic point of view; the second center, the Broca area, is a secondary motor region highly specialized in speech production, controlling the subtle and precise movement of the tongue, lips, and vocal cords.

The uncinate fasciculus is the last fasciculus to fully develop in the cerebrum. This means that it is not yet developed in children and teenager. It extends from the forward part of the frontal lobe (orbitofrontal cortex) to the temporal lobe, linking decision-making and bebavior-modulating areas in the frontal lobe with the auditory region in the temporal lobe and the hippocampus, which is contained within this lobe. Since the hippocampus, which is connected to the amigdala, is a center of emotion, the uncinate fasciculus makes it possible for the frontal lobe to inhibit, control and/or modulate emotional behavior to make us successfully adapt and behave appropriately in a social or dangerous situation. So, the uncinate fasciculus is what makes us behave as grown-ups or mature adults.