When neuroscientists attempt to understand our species' technological genius, they typically focus their attention on the human neocortex. Indeed, the neocortex—the most recently-evolved region of the brain—looms so large in study of human consciousness and brain function that the Blue Brain Project, which aspires to build a synthetic brain, has as its first goal the simulation of the human neocortex.
New research, however, suggests that humanity's technological prowess isn't limited to that brain region alone. Researchers Robert Barton of Durham University and Chris Venditti of the University of Reading just published findings that indicate that the rapid expansion of the cerebellum—the part of the brain largely responsible for movement control—in humans and great apes was vital to humanity's development of the technical skill for making and using tools.
In their paper, " Rapid evolution of the cerebellum in humans and other great apes," published in Current Biology, Barton and Venditti report that the cerebellum expanded up to six times faster in human and ape evolution than previously estimated. By comparison, the rapid evolution of the human and the great ape cerebellum left other primates in the dust. They believe this rapid evolution set the human and great ape species—both of which make and use tools—apart from other primates.
"An expanded neocortex has generally been considered to be the substrate of higher cognition and has been linked in particular to the evolution of social intelligence," the study reports. "Human evolution was, however, characterized by increasing technological complexity as well as social complexity. The cerebellum is particularly likely to have played a role in technological complexity, through its involvement in the learning of sensory-motor skills, imitation, and production of complex sequences of behaviors, such as those involved in making and using tools."
"The confluence between different lines of evidence," Barton and Venditti wrote, "namely the cognitive neuroscience of cerebellar function and its role in complex sequence production and comprehension, including language, observations of technical intelligence and tool use in hominins and other great apes, the comparative anatomy of cerebellar fine structure, and our documentation of rapid cerebellar expansion, thus suggests that the current, almost exclusive emphasis on the forebrain as the locus of advanced cognitive functions may be exaggerated and points to a key role for the cerebellum in human cognitive evolution."
The researchers also noted that while the neocortex is larger than the cerebellum in humans and other mammals, this is likely to do with the body size required to house it. Even so, the cerebellum is equipped with far more neurons than the neocortex.
"In humans, the cerebellum contains about 70 billion neurons—four times more than in the neocortex," Barton said. "Nobody really knows what all these neurons are for, but they must be doing something important."
As Johns Hopkins researchers noted in a 1997 paper, the cerebellum is essentially a "powerful computer" and an "enormously impressive mechanism." Like a computer, the human cerebellum can take in massive amounts of information from many regions of the brain and output them to many others. The Hopkins researchers also noted that the cerebellum can automate motor, mental, and sensory tasks, freeing up the conscious brain to take on other tasks.
In 2008, Columbia University scientists marveled at the cerebellum found in humans versus those found in primates. "[F]ossil endocast data suggest that recent human evolution was characterized by a burst of cerebellar expansion that was unmatched by a parallel increase in neocortex size," the Columbia researchers reported. "Beyond relative cerebellar size, humans also differ from other primates in the size and shape of the cerebellar dentate nucleus."
Building on such studies for their own research, Barton and Venditti concluded that technical intelligence was likely as important as social intelligence in humanity's cognitive evolution.
"Our results highlight a previously unappreciated role of the cerebellum in ape and human brain evolution that has the potential to refocus researchers' thinking about how and why the brains in these species have become distinct and to shift attention away from an almost exclusive focus on the neocortex as the seat of our humanity," said Barton.
Barton and Venditti believe that this research will open up "a new frontier for investigations into the neural basis of advanced cognitive abilities."