Hearing voices: a brain out of sync?
Some 200 milliseconds before you speak, brain cells in your motor cortex fire in concert, predicting the sounds you are about to produce. This electrical discharge instructs your auditory cortex to disregard any matching signals coming from your ears, which keeps you from being distracted by the sound of your own voice.
But the story may be different for patients with schizophrenia, as Judith Ford, Ph.D., and collaborators suggest in the March issue of the American Journal of Psychiatry. The researchers found that brain activity synchronized shortly before the onset of speech, possibly reflecting communication between the motor and sensory cortex. However, in patients with severe auditory hallucinations, this pre-speech synchronization is weaker, and the brain’s reaction to self-generated speech is not dampened: patients who hear voices seem less able to recognize their own.
Next on the authors’ list is to repeat the study for the “inner speech” that accompanies thinking to see whether a lack of synchronization may cause patients with schizophrenia to mistakenly perceive their inner thoughts as external voices.