Processing of vocalizations in humans and monkeys: a comparative fMRI study

Area of Science:

• Neuroscience
• Comparative Cognition
• Evolutionary Biology

Background:

• Acoustic signals are crucial for social interactions in many species.
• The neural basis and evolutionary trajectory of vocal communication remain largely unexplored.
• Functional neuroimaging is beginning to reveal the brain networks involved in auditory processing.

Purpose of the Study:

• To compare the cortical networks underlying vocalization processing in humans and macaque monkeys.
• To investigate the neural substrates differentiating human speech processing from general vocal sound perception.
• To explore the evolutionary recruitment of brain regions, such as the superior temporal sulcus (STS), for language.

Main Methods:

• Application of functional magnetic resonance imaging (fMRI) in both humans and macaque monkeys.
• Presentation of identical auditory stimuli, including vocalizations, to both species.
• Analysis of fMRI activity maps to identify species-specific and shared neural responses.

Main Results:

• Similar early auditory processing was observed in both species within the lateral sulcus.
• Monkeys exhibited comparable responses to conspecific calls and human vocal sounds in the lateral sulcus and superior temporal gyrus (STG).
• Humans showed a distinct preference for human vocalizations, particularly speech, in the STG and STS; the STS and Broca's region were highly responsive to intelligible speech.

Conclusions:

• The human brain, specifically the STS, has undergone significant evolutionary adaptation for processing complex vocalizations like speech.
• While early auditory pathways are conserved, higher-level processing of vocalizations diverges between humans and macaques.
• The specialized repertoire of human vocal communication, especially language, likely drove the recruitment of extensive temporal lobe regions.