Language Center - Current Scientific Consensus

Current Scientific Consensus

New medical imaging techniques such as PET and fMRI have allowed researchers to generate pictures showing which areas of a living brain are active at a given time. In the past, research was primarily based on observations of loss of ability resulting from damage to the cerebral cortex. Indeed, medical imaging has represented a radical step forward for research on speech processing. Since then, a whole series of relatively large areas of the brain have been found to be involved in speech processing. In more recent research, subcortical regions (those lying below the cerebral cortex such as the putamen and the caudate nucleus) as well as the pre-motor areas (BA 6) have received increased attention. It is now generally assumed that the following structures of the cerebral cortex near the primary and secondary auditory cortexes play a fundamental role in speech processing:

• Superior temporal gyrus (STG): morphosyntactic processing (anterior section), integration of syntactic and semantic information (posterior section)
• Inferior frontal gyrus (IFG, Brodmann area (BA) 45/47): syntactic processing, working memory
• Inferior frontal gyrus (IFG, BA 44): syntactic processing, working memory
• Middle temporal gyrus (MTG): lexical semantic processing

The left hemisphere is usually dominant in right-handed people, although bilateral activations are not uncommon in the area of syntactic processing. It is now accepted that the right hemisphere plays an important role in the processing of suprasegmental acoustic features like prosody.

Most areas of speech processing develop in the second year of life in the dominant half (hemisphere) of the brain, which often (though not necessarily) corresponds to the opposite of the dominant hand. 98 percent of right-handed people are left-hemisphere dominant, and the majority of left-handed people as well.