.: Scientific Highlight of the Year

Whose voice is that? Evolutionarily conserved voice-recognition regions in the brains of primates.

How does the brain recognize voices? Scientists at the Max-Planck Institute for Biological Cybernetics in Tübingen, Germany, now take us closer to an answer with their discovery of a "voice" region in the brain of a nonhuman primate¹.

Monkeys, like humans, rely on members of their species for social interactions and survival. Vocal communication facilitates interaction, warns the animals of danger and keeps the group together during group movement. Behaviorally we have known that monkeys are exquisitely sensitive to vocalizations from members of their species and can vocally recognize individuals. What was not clear is whether there are dedicated neuronal regions in the primate brain for processing species-specific vocalizations.

The research group led by Christopher Petkov in the laboratory of Nikos Logothetis used a non-invasive imaging technique, which has become a standard tool for understanding human brain function, to image macaque monkeys, one of our distant primate relatives. In their study the authors describe the discovery of a monkey "voice" region, a part of the brain that is important for individuals to recognize vocalizations from other members of their species¹.

The study shows that the voice region wasn't active to just any sound. Instead, this brain region preferred vocalizations from members of the species, or those sounds that hold special meaning for members of a species. Additionally, the scientists found that this voice region is also sensitive to vocal identity. Consequently, the scientists conclude that this region supports multiple vocal recognition abilities, such as identifying the acoustical signature or the ‘voice' of the species and the ‘voices' of different individuals.

Because the authors of the study used the same imaging technology that is commonly used to study human brain function, their study allowed them to make direct links to human imaging work. The authors observed that the monkey voice region is similar in function to the known human voice region^{2, 3}. This observation establishes the human and monkey voice regions as having been evolutionarily conserved and suggests that more animal species have voice regions.

This study also challenges the idea that there is little to be learned from other animals about human communication and has important implication for how human language evolved. Petkov and colleagues note that the human-voice region appears to have repositioned to a different anatomical position in the brain than where they observed the monkey region. This means that the comparative study of the voice regions in both humans and monkeys could disclose not only how evolution affected the voice regions but also how the neighboring human speech and language regions were affected by the brain differentiation that gave rise to human language and cognitive abilities. Second, the observation of clear evidence for vocal-recognition regions in the brains of living nonhuman primates supports the notion that human language evolved gradually. It now seems more likely that the vocal-recognition systems of nonhuman primates served as a neuronal basis upon which human verbal recognition and language evolved, rather than a striking evolutionary event which occurred recently within our human lineage and cannot be studied in extant nonhuman primates.

These findings in monkeys and the link to the human work are also important because the monkeys can now help us to understand the neuronal mechanisms by which listeners recognize communication signals, in ways that cannot be easily studied in humans. This could provide pathways for understanding and treating communication disorders, such as phonagnosia, a deficit where human patients fail to recognize the voice of someone that they know, or age-related problems in verbal recognition.

References

1. Petkov, C.I., et al. A voice region in the monkey brain. Nat Neurosci 11, 367-374 (2008).

2. Belin, P. & Zatorre, R.J. Adaptation to speaker's voice in right anterior temporal lobe. Neuroreport 14, 2105-2109 (2003).

3. Belin, P., Zatorre, R.J., Lafaille, P., Ahad, P. & Pike, B. Voice-selective areas in human auditory cortex. Nature 403, 309-312 (2000).

Chris Petkov is conducting comparative studies of brain function that reveal conserved brain function in primates, with an emphasis on vocal communication. He received a B.A. in Psychology and Biology at California State University and a Ph.D. in neuroscience at the University of California at Davis. In his doctoral work he studied how neurons stabilize perception in noisy environmental settings and used imaging techniques to understand both normal and impaired human brain function. He is currently a postdoctoral fellow at the Max-Planck Institute for Biological Cybernetics in Tübingen, Germany with Dr. Nikos Logothetis where he is using advanced magnetic-resonance imaging and neurophysiological technologies. For this work he was the recipient of fellowships from the Alexander von Humboldt and the Max-Planck Societies. In the fall of 2008 he will join the Institute of Neuroscience at Newcastle University, England, where his laboratory will pursue the neurobiology of communication disorders.