Broca's and Wernicke's Areas

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Human Uniqueness Compared to "Great Apes": 
Relative Difference
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It has been suggested that Broca’s and Wernicke’s areas are unique to humans. Broca’s and Wernicke’s areas are cortical areas specialized for production and comprehension, respectively, of human language. Broca’s area is found in the left inferior frontal gyrus and Wernicke’s area is located in the left posterior superior temporal gyrus. Non-human primates (both apes and monkeys) possess cortical areas that are in similar locations to and have similar cytoarchitecture as Wernicke’s and Broca’s areas in humans, and are probably homologous to them. The putative macaque homologue of Broca’s area, known as area 44 or area F5, shares functional properties with human Broca’s area. In both species, the region represents non-linguistic hand and mouth movements. Evidence also suggests that both species may have mirror neurons in this region that are involved in understanding the actions and intentions of others. In both macaques and humans, this region is likely involved in producing orofacial expressions and in understanding the intentions behind orofacial expressions of others. In humans, it has evolved an additional communicative function, namely speech production. However, it does not appear to be involved in monkey vocalizations, which are instead mediated by limbic and brainstem areas. Regarding Wernicke’s area, evidence suggests that the left superior temporal gyrus is specialized for processing species-specific calls in macaques just as it is specialized for speech comprehension in humans, although the specific anatomical focus of this macaque specialization is still in doubt. Despite substantial anatomical and functional similarity between Wernicke’s and Broca’s areas in humans and their homologues in non-human primates, there are noteworthy differences in connectivity between the two regions, with humans possessing markedly stronger and more widespread connectivity via the arcuate fasciculus pathway. In fact, tract tracing studies suggest that the dominant projection of the macaque homologue of Wernicke’s area is to dorsal prefrontal cortex rather than to Broca’s area homologue. 

Timing

Timing of appearance of the difference in the Hominin Lineage as a defined date or a lineage separation event. The point in time associated with lineage separation events may change in the future as the scientific community agrees upon better time estimates. Lineage separation events are defined in 2017 as:

  • the Last Common Ancestor (LCA) of humans and old world monkeys was 25,000 - 30,000 thousand (25 - 30 million) years ago
  • the Last Common Ancestor (LCA) of humans and chimpanzees was 6,000 - 8,000 thousand (6 - 8 million) years ago
  • the emergence of the genus Homo was 2,000 thousand (2 million) years ago
  • the Last Common Ancestor (LCA) of humans and neanderthals was 500 thousand years ago
  • the common ancestor of modern humans was 100 - 300 thousand years ago

Probable Appearance: 
50,000 thousand years ago
Definite Appearance: 
100 thousand years ago
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References

  1. Sexual dimorphism of Broca's region: More gray matter in female brains in Brodmann areas 44 and 45, Kurth, Florian, Jancke Lutz, and Luders Eileen , Journal of Neuroscience Research, 2017, Volume 95, Issue 1-2, p.626 - 632, (2017)
  2. Redefining the role of Broca's area in speech., Flinker, Adeen, Korzeniewska Anna, Shestyuk Avgusta Y., Franaszczuk Piotr J., Dronkers Nina F., Knight Robert T., and Crone Nathan E. , Proc Natl Acad Sci U S A, 2015 Mar 3, Volume 112, Issue 9, p.2871-5, (2015)