The neural circuitry underlying primate calls and human language |
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Authors: | T W Deacon |
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Institution: | (1) Biological Anthropology, Harvard University, 02138 Cambridge, MA, USA |
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Abstract: | There are significant structural and functional differences between primate calls and human speech. In addition, these two
forms of vocal communication appear to largely depend on nonhomologous brain structures. However, an analysis of the underlying
axonal circuitry of these brain systems suggests that there are significant interrelationships between them, both in functional
and in evolutionary terms. Based on both primate neuroanatomical studies and humanin vivo mapping studies it is argued that the ventral prefrontal area is the critical link, both functionally and anatomically between
these distinct vocal systems. A model of human brain evolution with respect to language is proposed in which limbic-midbrain
vocalization circuits became progressively subordinated to the activity of prefrontal-midbrain and frontalmotor circuits for
regulating facial gesture, skilled oral food manipulation, and conditional association learning. Quantitative and developmental
data are used to suggest that this resulted from the relative enlargement of prefrontal areas and the consequences this has
on the relative proportions of different corticomidbrain and diencephalic-midbrain projections. Although humans exhibit a
significantly reduced call repertoire, it is argued that the display-vocalization circuits that play the central role in all
other primate communication have neither been eliminated, supplanted nor suppressed by language systems. They have instead
become integrated into the more distributed language circuits and play a ubiquitous though subordinate role in all normal
language processes. |
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