Increase Volume of Brain with the Sophistication of Speech

1. Investigating the anatomical origins of language in fossil humans

Different areas of brain – cerebral cortex

Increase volume of brain with the sophistication of speech

Intro Bit -

• Undergone a substantial change in brain size and organization the last common ancestor of the Homo Sapiens lineage
• This results in a marked difference between living apes and humans in terms of linguistic expression
• It can be seen that the last common ancestors to humans appeared to have a brain size of approximately 300-400g that display several phylogenetic specializations of developmental, anatomical organization and biochemical function
• These contribute to the enhancement of behavioural flexibility and social cognition
• As shown by this evolutionary precursor, it is evident that the modern human may be conceived as a mosaic of traits inherited from a common ancestor
• These modern human-specific cognitive ad linguistic adaptations appear to be correlated with the enlargement of the neocortex and related structures
• In addition to this, the unique brain growth trajectory of modern humans has made a significant contribution to the cognitive and linguistic ability of our species.
• Establishing a clear causal link between evolutionary changes in brain structure and the emergence of species-specific behaviour is complicated.
• Anatomical homology does not necessarily entail functional similarity

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2409100/

Brain size in relation to evolution of linguistic capacity

• Humans capacity for language cannot be entirely explained by brain size
• Human brain specializations that potentially support our capacity for language includes firstly, wider cortical minicolumns n both Broca’s and Wenicke’s areas compared with great apes
• Secondly, leftward asymmetries in Broca’s area volume and Wernicke’s are minicolumns width that are not found in apes
• Thirdly arcuate fasciculus projections beyond Wernicke’s area to a region of expanded association cortex in the middle and inferior temporal cortex involved in processing word meanings
• These arcuate fasciculus pathway connecting Broca’s and Wernicke’s area of the brain
• It is involved in language and is markedly expanded in human evolution
• Broca’s area – region in left inferior frontal cortex is responsible for speech production
• Broca’s area also mediates communication in non-human primates
• Obvious functional differences between human and chimpanzees Broca areas – in motor aspects of speech and with syntax
• Largely supported by underlying anatomical differences
• Wider cortical minicolumns in humans Broca’s area than in great apes
• Known that Broca’s area asymmetry is not present in Chimpanzees
• Wernicke’s area – posterior portion of the left superior temporal gyrus essential for speech comprehension
• Human Wernicke’s area not found in other non-human homologue include phonological processing
• Perhaps – other primate species lack human language skills due to lack of homology between Wernicke and Broca’s areas as in humans.
• However, when defined based on arrangement of cells and types of tissues in the cerebral cortex and shared non-linguistic functional properties – homologues can be identified in non-human primates.
• Leads to question of wether there might be microstructural differences within these areas between humans and non-human primates
• Brain size of humans = 1400cc – far exceeds size of other living primate species

Source: http://www.sciencedirect.com.ezproxy.lib.monash.edu.au/science/article/pii/S0959438814000816