One compelling study used PET imaging to watch what is going on in the brain during inner speech. As expected, this showed activity in the classic speech production area known as Broca’s area. But also active was Wernicke’s area, the brain region for language comprehension, suggesting that not only do the brain’s speech areas produce silent inner speech, but that our inner voice is understood and interpreted by the comprehension areas. The result of all this activity, I suggested, is the narrative self.
Since then, much more neuro-imaging data has supported this idea. Sukhwinder Shergill, a psychiatrist at King’s College London, has contributed mightily, investigating the neural bases of schizophrenia symptoms, including auditory hallucinations. By generating and monitoring inner speech in ingenious ways, his functional MRI studies consistently show activity in neural areas involved in speech production, comprehension and internal monitoring during silent inner speech. This fits nicely with Gazzaniga’s idea about the left hemisphere interpreter’s role in creating the autobiographical self.