Sunday, February 18, 2018
High Dopamine May Cause Psychosis Patients to Focus More on Expectations
A new study finds that schizophrenia patients with auditory hallucinations often hear what they expect to hear. In fact, the hallucinations may be an extreme version of a perceptual distortion quite common among healthy people.
Research has long established that people who experience hallucinations and other psychotic symptoms tend to have elevated dopamine, but the exact link between dopamine and hallucinations has remained unclear.
In the new study, researchers at Columbia University Irving Medical Center (CUIMC) and New York State Psychiatric Institute (NYSPI) found that elevated dopamine could be causing some patients to rely more on expectations, which could then result in hallucinations.
The findings help explain why treatments targeting the production of dopamine could help alleviate this condition.
“Our brain uses prior experiences to generate sensory expectations that help fill in the gaps when sounds or images are distorted or unclear,” said Guillermo Horga, M.D., Ph.D., assistant professor of clinical psychiatry at CUIMC and a research psychiatrist at NYSPI.
“In individuals with schizophrenia, this process appears to be altered, leading to extreme perceptual distortions, such as hearing voices that are not there. Furthermore, while such hallucinations are often successfully treated by antipsychotic drugs that block the neurotransmitter dopamine in a brain structure known as the striatum, the reason for this has been a mystery since this neurotransmitter and brain region are not typically associated with sensory processing.”
For the study, the research team designed an experiment that induced an auditory illusion in both healthy participants and participants with schizophrenia. They observed how building up or breaking down sensory expectations can modify the strength of this illusion. They also measured dopamine release before and after administering a drug that triggers the release of dopamine.
The findings show that the schizophrenia patients tended to perceive sounds in a way that was more similar to what they had been cued to expect, even when sensory expectations were less reliable and the illusions weakened in healthy participants.
This tendency to inflexibly hear what was expected became worse after they were given a dopamine-releasing drug, became more pronounced in participants with elevated dopamine release, and more apparent in participants with a smaller dorsal anterior cingulate (a brain region previously shown to track reliability of environmental cues).
“All people have some perceptual distortions, but these results suggest that excess dopamine can exacerbate our distorted perceptions,” said Horga. “Novel therapies should aim to improve the processing of contextual information by targeting the dopamine system or downstream pathways associated with modulation of perceptual processing, which likely include the dorsal anterior cingulate cortex.”
The study is published in the journal Current Biology.
Source: Columbia University Medical Center
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Screening All Adults for Hepatitis C is Most Cost-Effective Way to ID Those Infected
Screening all adults for hepatitis C (HCV) is the most cost-effective way to identify more people with the disease as well as improve patients’ health and quality of life, compared to the current recommendations of screening only certain populations.
Hepatitis C is a viral infection that causes liver inflammation and sometimes serious liver damage. Many people with HCV experience neuropsychiatric symptoms such as brain fog, confusion, irritability, difficulty concentrating, and fatigue. These symptoms make it difficult to carry on everyday tasks.
The Centers for Disease Control and Prevention (CDC) currently recommends HCV testing for people born between 1945 and 1965, the highest risk population in the U.S. However, recent statistics have shown a growing incidence rate of HCV among young people.
“Due in part to the opioid epidemic and the increase in injection drug use, the country has seen an increase in cases of HCV among young people,” says Benjamin Linas, M.D., co-senior author of the study and infectious disease physician at BMC and an associate professor of medicine at Boston University Medical Center. “The CDC could address this public health concern by recommending all adults receive a one-time HCV test.”
To address this gap in testing, researchers from Boston Medical Center, Massachusetts General Hospital (MGH), and Stanford University created a simulation model to estimate the effectiveness of HCV testing strategies among different age groups.
They compared the effects of testing four age brackets: current testing recommendations (those born between 1945 and 1965), testing people over 40 years old, testing people over 30 years old, and testing all adults over 18 years old. All strategies included the current recommendations for targeted testing of high-risk individuals, such as people who inject drugs.
The researchers discovered that, compared to current recommendations, screening all adults over 18 for HCV would identify more than 250,000 additional people with the disease, increase cure rates from 41 percent to 61 percent, and reduce death rates for HCV-attributable diseases by more than 20 percent. Overall, screening for all adults would increase life expectancy and quality of life while remaining cost-effective.
“When we expanded testing, the results were compelling,” says Joshua Barocas, M.D., lead author on the study, an infectious disease physician at MGH and an instructor in medicine at Harvard Medical School. “Changing the current recommendations could have a major public health impact, improving the quality of life for young people with HCV, and reducing death rates.”
The study pulled data from national databases, clinical trials, and observational cohorts to inform their simulation models, which took into account the same demographics and HCV epidemiology of the U.S. population.
Although all of the age-based strategies lowered costs associated with managing chronic HCV and advanced liver disease, the strategy of testing all adults was most effective. Even in a simulated scenario that required twice as much testing among uninfected people to identify the same number of HCV cases, the testing-all-adults strategy remained cost-effective.
“Testing all adults would lead to earlier diagnosis and treatment for many people, which would help to prevent cirrhosis and other long-term complications,” says Joshua Salomon, Ph.D., co-senior author of the study and professor of medicine at Stanford University. “Overall, when you consider both the better health outcomes and the reduced costs of managing long-term liver disease, expanded testing offers excellent value for money.”
Researchers say these findings should be considered by the CDC for future recommendations on HCV testing.
Source: Boston Medical Center
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