Early Left-Planum Temporale Asymmetry in newborn monkeys ( Papio anubis): A longitudinal structural MRI study at two stages of development

Highlights

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  Newborn baboons present a leftward Planum Temporale Asymmetry.

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  The proportion is similar to human newborns and adults.

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  As in human infants, the asymmetry strength increases across development.

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  These findings question early Planum Temporale Asymmetry as a human-specific marker for the prewired language-ready brain.

Abstract

The “language-ready” brain theory suggests that the infant brain is pre-wired for language acquisition prior to language exposure. As a potential brain marker of such a language readiness, a leftward structural brain asymmetry was found in human infants for the Planum Temporale ( PT), which overlaps with Wernicke's area. In the present longitudinal in vivo MRI study conducted in 35 newborn monkeys ( Papio anubis), we found a similar leftward PT surface asymmetry. Follow-up rescanning sessions on 29 juvenile baboons at 7-10 months showed that such an asymmetry increases across the two ages classes. These original findings in non-linguistic primate infants strongly question the idea that the early PT asymmetry constitutes a human infant-specific marker for language development. Such a shared early perisylvian organization provides additional support that PT asymmetry might be related to a lateralized system inherited from our last common ancestor with Old-World monkeys at least 25–35 million years ago.