If human evolution were akin to tinkering in a garage, one question would be whether the powerful thinking machine in our heads was built over time with new, upgraded equipment or re-modified old gears. Researchers recently took a stab at this issue by looking at the front part of our brain, which bestows cognitive abilities that sets us apart as humans, and compared it to the rhesus monkey’s anatomical equivalent. To their surprise, the two shared numerous physical similarities in this area, though crucial differences were also evident.
“It has been argued that to develop these abilities, humans had to evolve a completely new neural apparatus; however others have suggested precursors to these specialized brain systems might have existed in other primates," explained lead author, Dr. Franz-Xaver Neubert of the University of Oxford, in a press release.
Neubert and team made the comparison by using a non-invasive magnetic scanner that detailed the connectivity and architecture of the brains of 25 humans and macaques. They focused on a region called the ventrolateral frontal cortex (vlFC), which is a hub for higher order thinking, such as flexible decision-making. The similarities in anatomical layout in this region, the authors posed, suggest that part of what makes us distinctly human depends on the same neuronal tools that existed during our more primitive days when they were used for different purposes.
Yet the MRI scans also detected fundamental differences between the humans and monkeys with regard to this frontal brain region. Specifically, the MRI showed that the vlPC was wired up differently with parts of the brain that are designated for hearing. "This could explain why monkeys perform very poorly in some auditory tasks and might suggest that we humans use auditory information in a different way when making decisions and selecting actions," Neubert explained.
Another notable difference involved the human brain region called the frontal pole, which is important for strategic planning, decision-making, and multi-tasking. This area is important for human cognitive function but was completely absent in monkeys, which made sense to the authors. Altogether, the authors concluded in Neuron that they identified “fundamental similarities but also striking differences between monkeys and humans in the way vlFC regions link with the rest of the brain.”
The significance of the research doesn’t only help in answering an evolutionary question. The authors pointed out that some regions of the vlFC that were similar in humans and monkeys have also been implicated in various psychiatric disorders, including attention deficit hyperactivity disorder (ADHD), obsessive compulsive disorder, and substance abuse. A deeper understanding of how these networks have changed over evolutionary time might shed light on how they contribute to these disorders and could even guide appropriate therapeutic strategies.
Source: Neubert F, Mars RB, Thomas AG, et al. Comparison of Human Ventral Frontal Cortex Areas for Cognitive Control and Language with Areas in Monkey Frontal Cortex. Neuron. 2014.