For those who live with schizophrenia, the sound of voices — voices that no one else can hear — can be an overwhelming and persistent part of daily life. But the mystery of why these hallucinations happen has stumped scientists for decades. Now, researchers believe they may be closer to solving this riddle.
A new study suggests that the cause of these phantom voices lies in the brain’s inability to recognize its own speech signals. The findings could open the door to treatments that go beyond medications, offering new hope to the millions of people who struggle with schizophrenia worldwide.
Scientists are finally beginning to understand the specific brain mechanisms that cause auditory hallucinations. And this could change the way we think about the disorder and how we treat it.
When the Brain Can’t Hear Itself
People with schizophrenia often report hearing voices that seem to come from somewhere outside themselves. These auditory hallucinations affect up to 80% of patients and are one of the hallmarks of the illness. But what’s happening in the brain to create this experience?
The answer may lie in the way the brain processes its own speech signals. Normally, when we prepare to speak, our brain generates a copy of the motor commands it uses to move our mouths and tongues. This copy, known as a “corollary discharge,” is sent to the auditory system to let it know that the sounds we are about to make are coming from us — not the outside world.
In people with schizophrenia, however, this system seems to malfunction. Using EEG monitors, the research team tracked brain activity in three groups of people: those with schizophrenia who experience auditory hallucinations, those with schizophrenia who don’t, and a control group of healthy individuals. The results were telling.
Both groups of patients with schizophrenia showed a disruption in their brain’s ability to predict the sound of their own voices before speaking. But for those who heard voices, something else was happening: a hyperactive efference copy — the signal that tells the body to vocalize. This overactive signal, researchers suggest, floods the auditory system, creating a chaotic jumble of internal sounds that the brain can’t properly filter out.
“People who suffer from auditory hallucinations can ‘hear’ sounds without external stimuli,” explained neuroscientists led by Fuyin Yang from Shanghai Jiao Tong University, who co-authored the study. “Impaired functional connections between motor and auditory systems in the brain mediate the loss of ability to distinguish fancy from reality.”
In short, the brain of someone experiencing hallucinations is overwhelmed by its own noise.
Voices from Within
It may seem abstract, but the mechanisms behind these hallucinations are something we all experience on a much smaller scale. Think about tickling. No matter how hard you try, you can’t tickle yourself. That’s because your brain predicts the sensation and dampens your response.
For people with schizophrenia, however, this internal suppression breaks down. Without the ability to filter out their own speech signals, their brains treat their inner thoughts as if they were external sounds — leading to the sensation of hearing voices.
The research builds on decades of work trying to explain why schizophrenia patients experience such profound distortions of reality. Earlier studies have pointed to disruptions in the brain’s motor systems, suggesting that misfired signals may be at the root of auditory hallucinations. But this new study goes a step further, identifying the specific signals that go awry.
These insights could be a game-changer for treating schizophrenia as they add a level of nuance to the condition that wasn’t available before.
“You can’t treat what you don’t understand,” Tom Whitford, a psychology professor at the University of New South Wales in Australia who was not involved in the research, told STAT. “It’s very worthwhile knowing exactly what aspect of that mechanism is not normal in people with schizophrenia,” he added.
A Future Without Medications?
Currently, schizophrenia is treated primarily with antipsychotic medications, which can have severe side effects and don’t work for everyone. Many patients are resistant to drug treatments, leaving them with few options for managing their symptoms.
But if the brain’s faulty signals are to blame for auditory hallucinations, there may be other ways to address the problem. Xing Tian and his colleagues believe that non-invasive treatments, such as transcranial magnetic stimulation (using a magnetic coil to influence the brain’s natural electrical activity), could help regulate brain activity and potentially silence the voices in patients who don’t respond to medication.
“Some patients are really resistant to drugs — maybe that’s because it’s hard to modulate the function network [with them],” said Xing Tian, the study’s lead author and an associate professor of Neural and Cognitive Sciences at NYU Shanghai. “If our theory is right, then using a non-invasive neuromodulation technique can alleviate the hallucinations.”
This research comes at a pivotal time for schizophrenia treatment. In recent months, the FDA has approved a new drug that could change how the disorder is treated, marking the first major advancement in decades. Coupled with these new insights into the brain’s role in hallucinations, the future for schizophrenia treatment may be brighter than it has been in years.
For the nearly 4 million people living with schizophrenia in the United States alone, that future can’t come soon enough. As researchers continue to peel apart the secret layers of the brain, the hope is that one day, those voices will finally fall silent.
The findings appeared in the journal PLOS Biology.
