A new study reveals a missing area of brain activity in people with schizophrenia. This lack explains the voices caused by schizophrenia.
Analysis of brain wave data suggests that a combination of two neurological functions could trigger . Researchers in China have found evidence of a breakdown in the ability to prepare the senses for words to be spoken. But this problem alone is not enough; another area that filters out the brain’s internal noise is also amplified in people with schizophrenia who experience disturbing auditory hallucinations.
Without self-noise suppression, and with amplified internal noise signals, things can get confusing in our minds.
“People who suffer from can ‘hear’ sounds without external stimuli. Impaired functional connections between motor and auditory systems in the brain mediate the loss of the ability to distinguish imagination from reality,” the team explains.
Neuroscientist Fuyin Yang, from Shanghai Jiao Tong University School of Medicine (China), and her colleagues examined the brains of 20 patients diagnosed with schizophrenia who experienced auditory hallucinations and compared them with 20 other patients also diagnosed with schizophrenia, but who did not have such hallucinations.
All these patients were taking antipsychotic medication and were in a stable condition for the duration of the experiment. Previous results from a group of people without schizophrenia were used as a control group.
What exactly leads to voices caused by schizophrenia?
Comparing brain activity data obtained by electroencephalograms in the three groups of patients, who were asked to hear and then say a short, pre-generated syllable, clear differences emerged. Both groups of patients with schizophrenia showed reduced activity associated with the brain’s ability to anticipate the sound of their voice before speaking a word. This function, known as corollary unloading, usually gives our senses a chance to anticipate sounds as self-generated and not treated as external.
This difference was also observed in mouse models of schizophrenia.
But only the patients who reported hearing voices had an overactive efferent copy (the motor signal that instructs the body to speak) that the team describes as an internal auditory representation. In healthy patients and those with schizophrenia who do not have auditory hallucinations, this signal is amplified only around the syllable that someone is preparing to say. But for those who hear voices, the amplification is more generalized, which basically increases the random internal noise of the brain.
“Imprecise activation of the efferent copy function … leads to variable amplification and sensitization of the auditory cortex,” the researchers write in the paper.
A step forward towards identifying new treatments
Auditory hallucinations appear to occur when uncontrolled corollary discharge misinterprets the neural activity caused by specifying the internal speech signal, Yang and his team explain.
This makes some people unable to differentiate between external voices and their own thoughts, blurring the line between internal and external reality.
With this new understanding of the mechanisms behind these auditory hallucinations, researchers hope to be able to develop better treatments.
This research was published in .
