Sub-vocal speech articulation. Highly self-aware individuals use inner speech significantly more frequently compared to less self-aware individuals. Brain-imaging studies have shown that inner speech is associated with activation of the left inferior frontal area. In contrast, the monitoring of one’s own speech (auditory verbal imagery), by means of imagining the sentences they generated when spoken in another person’s voice, is associated with increases in not only in the same area, but also in the left premotor cortex, the supplementary motor area and the left temporal cortex. The notion of internal speech is central to developmental process of internalization as detailed in the work of Lev Vygotsky (1896-1934): it reflects how language serves to promotes cognitive development of children in that they increasingly use internal speech to direct their own behavior as did parental speech previously.
See Brain (neuro-) imaging, Frontal cortex, Internalization, Premotor cortex, Supplementary motor area (SMA), Temporal lobe