Brain’s language pathway dates back at least 25 million years
21 April 2020
A research team involving UCL has discovered an earlier origin to the human language pathway in the brain, pushing back its evolutionary origin by at least 20 million years.
Previously, a precursor of the language pathway was thought by many scientists to have emerged more recently, about 5 million years ago, with a common ancestor of both apes and humans.
For neuroscientists, this finding, published in Nature Neuroscience, is comparable to finding a fossil that illuminates evolutionary history. However, unlike bones, brains do not fossilise. Instead neuroscientists need to infer what the brains of common ancestors may have been like by studying brain scans of living primates and comparing them to humans.
Lead author Professor Chris Petkov (Newcastle University) said: “It is like finding a new fossil of a long lost ancestor. It is also exciting that there may be an older origin yet to be discovered still.”
International teams of European and US scientists carried out the brain imaging study and analysis of auditory regions and brain pathways in humans, apes and monkeys.
They discovered a segment of this language pathway in the human brain that interconnects the auditory cortex with frontal lobe regions, important for processing speech and language. Although speech and language are unique to humans, the link via the auditory pathway in other primates suggests an evolutionary basis in auditory cognition and vocal communication.
Professor Petkov added: “We predicted but could not know for sure whether the human language pathway may have had an evolutionary basis in the auditory system of nonhuman primates. I admit we were astounded to see a similar pathway hiding in plain sight within the auditory system of nonhuman primates.”
The study also illuminates the transformation of the human language pathway. A key human unique difference was found: the human left side of this brain pathway was stronger and the right side appears to have diverged from the auditory evolutionary prototype to involve non-auditory parts of the brain.
The study relied on brain scans from openly shared resources by the global scientific community. It also generated original new brain scans that are globally shared to inspire further discovery.
Co-author Professor Fred Dick, director of the Birkbeck-UCL Centre for Neuroimaging, affiliated with UCL Psychology & Language Sciences, commented: "This study is a terrific example of the way cross-institutional and international collaboration can move science forward in a way that could never have been accomplished working in isolation."
Since the authors predict that the auditory precursor to the human language pathway may be even older, the work inspires the neurobiological search for its earliest evolutionary origin - the next brain ‘fossil’ - to be found in animals more distantly related to humans.
Joint senior author Professor Timothy Griffiths (Newcastle University and Honorary Principal at the Wellcome Trust Centre for Neuroimaging, UCL Queen Square Institute of Neurology) said: “This discovery has tremendous potential for understanding which aspects of human auditory cognition and language can be studied with animal models in ways not possible with humans and apes. The study has already inspired new research underway including with neurology patients.”
The study involved Newcastle University, Max Planck Institute for Cognitive and Brain Sciences, Birkbeck-UCL Centre for Neuroimaging, University of Texas, and University of Iowa.
- Balezeau, F., Wilson, B., Gallardo, G. et al. Primate auditory prototype in the evolution of the arcuate fasciculus. Nat Neurosci (2020). https://doi.org/10.1038/s41593-020-0623-9
- Birkbeck-UCL Centre for Neuroimaging
- Wellcome Centre for Human Neuroimaging, UCL Queen Square Institute of Neurology