A groundbreaking study published in the Proceedings of the National Academy of Sciences (PNAS) reveals a population of neurons in the monkey brain that are selectively responsive to human voices. This discovery, made by a team of scientists from the Timone Neuroscience Institute and the Institute of Language, Communication and the Brain, in Marseille, France, provides unprecedented insights into the neural mechanisms of voice perception and the evolution of communication systems in primates.
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Selective neurons for human voices
Using fMRI-guided electrophysiology, researchers recorded the spiking activity of individual neurons in the anterior temporal voice patches of two macaques. The study focused on the macaques' responses to various complex sounds, including vocalizations from multiple species. This approach allowed the team to discover unsuspected neurons highly selective for human voices.
In particular, they identified a subpopulation of neurons in the anterior temporal voice patches of macaque monkeys that are selectively responsive to human voices, separate from those that respond to macaque vocalizations. “We were really surprised to realize that many neurons were actually preferring human voice over macaque vocalizations”, says Dr Margherita Giamundo, the first author of the study. “They were even more numerous than neurons selective to macaque voices”.
The impact of the environment on neuronal development
The findings suggest that these neurons' selectivity is likely due to the macaques' extensive daily exposure to human voices. Dr. Pascal Belin, senior author, added, " I doubt these neurons exist in wild macaques, as they have not been in significant contact with human voices. The presence of neurons in macaques that specifically respond to human voices suggests a remarkable level of neural plasticity and adaptation, emphasizing the intricate bond between humans and animals." This discovery highlights the impact of environmental experience on neural development. “Human voices are more relevant than macaque calls for laboratory monkeys” says Dr Thomas Brochier, co-senior author of the study. “They can announce the arrival of the veterinarian (bad news), or of their assigned experimenter (good news).”
And in other closely related species?
This discovery is the first to demonstrate the evolution of neural mechanisms of vocal perception in primates in favor of human voice recognition, but other similar studies have been carried out on other species. “There are multiple examples of species analyzing the vocalizations of another – prey or predators – but this implies coevolution over million of years.“ says Dr Attila Andics, for ELTE University in Budapest, Hungary, who did not participate to the study but discovered areas sensitive to human voices in dogs. “It is likely that a mechanism similar to the one discovered in this study is also at play in our cats or dogs.”
The discovery challenges the purely evolutionary perspective of voice selectivity, suggesting that expertise and environmental exposure play crucial roles in shaping neural mechanisms. This research enhances our understanding of interspecies communication and the neural basis of auditory expertise, potentially shedding light on similar mechanisms in humans, such as musical expertise.
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Article published on June 13, 2024.
Reference: Giamundo, M., Trapeau, R., Thoret, E., Renaud, L., Nougaret, S., Brochier, T. G., Belin, P. A population of neurons selective for human voice in the monkey brain. 2024 J Proceedings of the National Academy of Sciences, e2405588121, 121, 25.
Header photo: Photo by Martijn Vonk on Unsplash.
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