Brain regions involved in speech production, mechanism and development

Speech might be one of the best inventions of human beings due to its critical communicative role in individuals' daily lives. Hence any study about it is valuable. To our knowledge, merely three studies focused on brain regions' associations with speech production were published more than eighteen years ago; furthermore, research on the brain areas associated with speech production is currently insufficient. The present review aims to provide information about all brain areas contributing to speech production to update the knowledge of brain areas related to speech production. The current study confirms earlier claims about activating some brain areas in the process; however, the previous studies were not comprehensive, and not all brain areas were mentioned. Three cerebral lobes are involved in the process, namely, the frontal, parietal and temporal lobes. The regions involved include the left superior parietal lobe, Wernicke's area, Heschl's gyri, primary auditory cortex, left posterior superior temporal gyrus (pSTG), Broca's area, and premotor cortex. In addition, regions of the lateral sulcus (anterior insula and posterior superior temporal sulcus), basal ganglia (putamen), and forebrain (thalamus) showed participation in the process. However, there was a different brain activation of overt and covert or silent speech (Broca's and Wernicke's areas). Moreover, mouth position and breathing style showed a difference in speech mechanism. In terms of speech development, the early postnatal years are important for speech development, as well as identifying three crucial stages of speech development: the pre-verbal stage, transition to active speech, and refinement of speech. In addition, during the early years of speech development, auditory and motor brain regions showed involvement in the process.