1. Behavioral and Cognitive Neuroscience, Department of Psychology, University of Iowa, Iowa City, Iowa 52242, USA
2. Laboratory of Neuropsychology, National Institute of Mental Health, Bethesda, Maryland 20892, USA
3. PET Department, Clinical Center, National Institutes of Health, Bethesda, Maryland 20892, USA

Correspondence to: Amy Poremba¹ Correspondence and requests for materials should be addressed to A.P. (Email: amy-poremba@uiowa.edu).

Abstract

It has often been proposed that the vocal calls of monkeys are precursors of human speech, in part because they provide critical information to other members of the species who rely on them for survival and social interactions^{1, 2}. Both behavioural and lesion studies suggest that monkeys, like humans, use the auditory system of the left hemisphere preferentially to process vocalizations^{3, 4}. To investigate the pattern of neural activity that might underlie this particular form of functional asymmetry in monkeys, we measured local cerebral metabolic activity while the animals listened passively to species-specific calls compared with a variety of other classes of sound. Within the superior temporal gyrus, significantly greater metabolic activity occurred on the left side than on the right, only in the region of the temporal pole and only in response to monkey calls. This functional asymmetry was absent when these regions were separated by forebrain commissurotomy, suggesting that the perception of vocalizations elicits concurrent interhemispheric interactions that focus the auditory processing within a specialized area of one hemisphere.

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