A person can experience visual hallucinations for many reasons, including consuming hallucinogenic substances or as a symptom of schizophrenia. But what are the brain mechanisms that explain hallucinations? Show
The Diagnostic and Statistical Manual of Mental Disorders (DSM-5) defines hallucinations as “perception-like experiences that occur without an external stimulus,” and which “are vivid and clear, with the full force and impact of normal perceptions, [though] not under voluntary control.” While we understand some of the circumstances that cause hallucinations — often in the context of substance misuse, mental health conditions, or neurological conditions — we are yet to find out the specifics of how these phenomena manifest in the brain. Recently, a team of researchers from the University of Oregon in Eugene has strived to uncover more information about how hallucinations affect brain activity. Their new study — conducted in mouse models — has revealed some surprises, which the investigators present in a paper that appears in the journal Cell Reports. The researchers worked with mice that they injected with a substance called 4-iodo-2,5-dimethoxyphenylisopropylamine (DOI), a hallucinogenic drug that investigators often use in animal research. Like other hallucinogenics, including LSD, DOI interacts with serotonin 2A receptors, which are involved in the serotonin reuptake process, though they may also play other, less well understood, roles in the brain. Once they gave the mice this drug, the researchers showed them several on-screen images and used various specialized methods to record neural (brain cell) activity in these rodents. The team found that contrary to what they had expected, the mice experienced reduced signaling between neurons in the visual cortex — the brain region largely responsible for interpreting visual information. The timing of the neurons’ firing patterns also changed. “You might expect visual hallucinations would result from neurons in the brain firing like crazy, or by mismatched signals,” notes senior author Cris Niell, who is an associate professor at the University of Oregon. “We were surprised to find that a hallucinogenic drug instead led to a reduction of activity in the visual cortex,” Niell adds. However, he continues, “[i]n the context of visual processing, […] it made sense.” The researchers also saw that the visual signals sent to the visual cortex were similar to signals sent in the absence of the drug, meaning that the brain still received the same visual information — yet was unable to process it correctly.
The team admits that studying hallucinations in mouse models is not ideal, since, of course, the animals cannot communicate their experience. However, the researchers note that the same types of drugs that cause hallucinations in humans also cause visible movement and behavioral changes in mice. This, the investigators explain, reasonably suggests that the same drugs alter brain activity in both animals and people. However, future studies should pay closer attention to the animals’ reactions to visual stimuli in the presence versus the absence of drugs. “I don’t feel like we’ve necessarily found the smoking gun for the entire underlying cause of hallucinations, but this is likely to be a piece of it,” Niell says. “The data we’ve collected will provide a foundation for additional studies going forward. In particular, we plan to use genetic manipulation to study particular parts of this circuit in more detail,” the senior researcher adds. And since previous research has suggested that serotonin 2A receptors — which the researchers also targeted in this study — are involved in schizophrenia, Niell and team would also like to find out whether their present findings may provide new perspectives regarding the treatment of this and other mental health conditions. People who have schizophrenia may hear voices or see things that aren’t real. But what happens inside the brain of someone who has schizophrenia? Scientists are working to understand that. They’ve found that people who
have the disorder may be more likely to have glitches in their genes that may disrupt brain development. There’s another key brain difference. Studies show that certain brain chemicals that control thinking, behavior, and emotions are either too active or not active enough in people with schizophrenia. Doctors also believe the brain loses tissue over time. And imaging
tools, like PET scans and MRIs, show that people who have schizophrenia have less “gray matter” -- the part of the brain that contains nerve cells -- over time. This research is helping efforts to develop better treatments for people who have this condition. Doctors don’t know what
causes schizophrenia. It could be passed down in families, but not everyone who has schizophrenia has a close relative (like a parent, brother, or sister) with the condition. Some researchers believe that problems with brain development may be partly responsible for schizophrenia. Others believe that inflammation in the brain may damage cells that are used
for thinking and perception. Many other things could also play a role, including: Scientists don’t know if these things trigger the disorder. But they do know that schizophrenia tends to show up in people around late adolescence or early adulthood. It usually causes a similar set of symptoms, but it can happen differently from person to
person. Two brain chemicals, dopamine and glutamate, carry messages to cells along brain pathways that doctors believe control thinking, perception, and motivation. Dopamine gets a lot of attention in brain research because it’s been linked to addiction. It also plays a role in other psychiatric and movement disorders, like Parkinson’s disease. In schizophrenia, dopamine is tied to
hallucinations and delusions. That’s because brain areas that "run" on dopamine may become overactive. Antipsychotic drugs stop this. Glutamate is a chemical involved in the part of the brain that forms memories and helps us learn new things. It also tells parts of the brain what to do. One study
found that people who are at risk for developing schizophrenia may have too much glutamate activity in certain areas of the brain at first. As the disease progresses, those brain areas may have too little glutamate activity. Doctors are working to find out how brain circuits that use these chemicals work together or are related to each other. Thanks to technology, doctors can see changes in specific areas of
the brain. They can also map the possible loss of brain tissue. One study showed that brain tissue loss in young people at risk of developing the illness was linked to psychotic symptoms like hallucinations. Another study compared MRI pictures of the brains of youths about age 14 who had no symptoms of schizophrenia with those who did. It found that the teens who had symptoms lost more brain tissue over a 5-year period than the others. Research shows that adults who have schizophrenia also may lose gray matter. The Default Mode NetworkWhen we’re just hanging out -- the dishes are done, we’ve finished our homework, or we've completed a tough project at work -- our thoughts are free to roam. This “default mode” allows us time to daydream, reflect, and plan. It helps us to process our thoughts and memories. Scientists call this the default mode network. When we’re not focused on a given task, it “lights up." If you have schizophrenia, your default mode network seems to be in overdrive. You may not be able to pay attention or remember information in this mode, one study shows. OutlookResearchers are working on new medications for the disorder. At least one tackles the glutamate factor. People with schizophrenia have also had some positive results using sarcosine, a chemical that is thought to regulate glutamate. But doctors aren’t sure whether it could help over the long term. So although schizophrenia has no cure and sometimes may get worse over time, the right medications, combined with therapy, can help control the symptoms. What part of the brain is responsible for hallucinations?Current neuroscience evidence suggests several brain areas are involved in the generation of hallucinations including the sensory cortex, insula, putamen, and hippocampus.
What causes hallucination in schizophrenia?There is evidence that in patients with schizophrenia there is impaired modulation of thalamocortical gamma activity by external sensory input, allowing attentional mechanisms to play a preponderant role in the absence of sensory input. This may lead to hallucinations.
What part of the brain is affected in schizophrenia?Schizophrenia is associated with changes in the structure and functioning of a number of key brain systems, including prefrontal and medial temporal lobe regions involved in working memory and declarative memory, respectively.
What part of the brain is responsible for delusions in schizophrenia?Notably, delusions correlated positively with the difference of the functional connectivity of the right hippocampus with the frontal lobe, suggesting that alterations of fronto-limbic novelty processing may contribute to the pathophysiology of delusions in patients with acute psychosis.
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What part of the brain causes hallucinations in schizophrenia
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