The brain does not merely recognize the human voice. A study from the University of Geneva (UNIGE) shows that certain areas of our auditory cortex specifically react to the vocalizations of chimpanzees, our closest cousins.
Published in the journal
eLife, these results suggest the existence of brain sub-regions particularly sensitive to the vocalizations of certain primates. This discovery opens a new perspective on the origin of vocal recognition and could shed light on the mechanisms behind the development of language.
When female and male participants heard chimpanzee vocalizations, this response was clearly distinct from that triggered by bonobos or macaques.
© L. Ceravolo
Our voice is a fundamental signal for social communication. In humans, a large part of the auditory cortex is dedicated to analyzing it. But do these skills have older roots?
To find out, scientists from the Faculty of Psychology and Educational Sciences (FPSE) at UNIGE adopted an approach based on species evolution. By comparing the neuronal processing of vocalizations emitted by species close to humans, such as chimpanzees and bonobos, or more distant ones like macaques, it is indeed possible to observe what our brain shares, or not, with that of other primates. This method allows exploring the emergence of the neural bases of vocal communication, long before the appearance of language.
These results could contribute to a better understanding of the development of vocal recognition, and even language, in children.
Visualizing vocalizations
The team presented vocalizations from four species to 23 participants: humans, as a control; chimpanzees, close to us both genetically and acoustically; bonobos, also genetically close, but whose vocalizations more resemble bird songs; and finally macaques, more distant from humans on both counts. Using functional magnetic resonance imaging (fMRI), the scientists analyzed the activity of the auditory cortex. "Our goal was to verify whether a sub-region specifically sensitive to primate vocalizations existed," explains Leonardo Ceravolo, scientific collaborator and lecturer at the FPSE and first author of the study.
This is precisely what the research team observed. A region of the auditory cortex, known as the "superior temporal gyrus," involved in processing sounds, including language, music, and emotions, activates in response to the vocalizations of certain primates. "When female and male participants heard chimpanzee vocalizations, this response was clearly distinct from that triggered by bonobos or macaques."
This specificity is all the more remarkable given that bonobos, although genetically as close to us as chimpanzees, produce vocalizations that are very different acoustically. It is therefore the double proximity, both evolutionary and acoustic, that seems to determine the human brain's response.
Implications for understanding language evolution?
This discovery opens interesting avenues for the study of the evolution of the neural bases of communication. It suggests that certain regions of the human brain may have retained, over the course of evolution, a sensitivity to the vocalizations of close cousins. "We already knew that animal brain areas reacted specifically to the voice of their conspecifics. But here, we show that a region of the adult human brain, the anterior superior temporal gyrus, is also sensitive to non-human vocalizations," emphasizes Leonardo Ceravolo.
These results reinforce the hypothesis that certain vocal processing abilities are shared between humans and great apes, and thus predate the appearance of articulated language. They could also contribute to a better understanding of the development of vocal recognition, and even language, in children, for example by helping to explain how babies manage to recognize the voices of their close ones while still in utero.