The homologue of the arcuate beam (a structure that connects the two main speech centre in the cortex) appeared at the common ancestors of monkeys and apes, that is at least 25 million years ago, reported in Nature Neuroscience. Until now it was thought that this structure was only about five million years ago.
To talk, you need to clearly control the movements of the muscles of the larynx, tongue and other anatomical structures. The area of the cerebral cortex that deals with that, called the Broca’s arealocated in inferior frontal gyrus and is part of the motor cortex. You also need to understand what the sound turned out (and what others say). For this is Wernicke’s area — area of the auditory cortex, the part of the superior temporal gyrus. Usually, both areas are located in the left hemisphere, and the structures in the other hemisphere at least are associated with it.
To coordinate areas of Broca and Wernicke in humans allows equity bundle — a group of nerve fibers, along which information from the auditory cortex is transmitted to the motor and Vice versa. If it is damaged, the person cannot repeat the words that I heard. Equity the beam is part of the so-called dorsal path. Besides him there are ventral, but he plays a slightly different role.
The chimpanzee is the homologue of the arcuate beam, although to produce sounds similar to human speech, they can’t. This nerve fibers connecting the inferior frontal gyrus from the middle temporal gyrus. Thus, it can be assumed that the structure began to develop in the common ancestor of humans and apes, and he lived about five million years ago. From nonhuman apes, such as macaques, such a homologue has not been well established: they have no middle temporal gyrus.
Nevertheless, neuroscientists led by Chris Petkov (Petkov Chris) from Newcastle University tried to clarify whether non-human structures which could give rise arcuately beam. To do this, they analyzed data from diffusion magnetic resonance imaging (insfcs) of three awake macaque brain, and similar information on macaque brain postmortem (i.e., after the death of the animal).