Applying mild electrical stimulation to an area of the brain associated with cognitive control helps people with schizophrenia to recognize errors and adjust their behavior to avoid them as much as it helps healthy subjects do so, according to a new study by Vanderbilt psychologists. The research was published June 29 in the Proceedings of the National Academy of Sciences.
One of the core symptoms of schizophrenia is poor cognitive control -- a constellation of abilities including working memory, attention, focus and error-monitoring. Error-monitoring can be measured by "post-error slowing" -- the almost imperceptible pause healthy people take after committing a mistake, like making a typo, in order to avoid doing it again. "It has been known for decades that error-monitoring is reduced in individuals with schizophrenia," said Sohee Park, Gertrude Conaway Vanderbilt Professor of Psychology, who contributed to the research. "This impairment has been extremely difficult to remediate."
An important brain area involved in cognitive control is the medial frontal cortex. In previous research, lead author Robert Reinhart, a graduate student in psychology, was able to improve post-error slowing in healthy individuals by applying a very safe, low-voltage electric current -- transcranial direct stimulation, or tDCS -- to the medial-frontal cortex of the brain. He wanted to see if people with schizophrenia could benefit as well.
First, participants donned EEG monitors and performed a challenging cognitive control task specifically designed to trip them up. "We saw a beautiful burst of low-frequency activity [from the medial-frontal cortex] right after someone made a mistake," said Reinhart. "But it was deficient in our patients with schizophrenia."
In healthy individuals, these theta waves were steady and synchronized, but in people with schizophrenia, the waves were weak and disorganized, suggesting that they were having a harder time processing the mistake. And the subjects' behavior bore that out -- the healthy subjects slowed down by a few milliseconds when they made mistakes and did better in the next round, while the subjects with schizophrenia did not.
After tDCS, the picture was dramatically different. The electrical stimulation to the scalp significantly improved the strength and synchrony of the brain waves in both groups but most notably in people with schizophrenia. "We found that medial-frontal stimulation resulted in normalization of patients' post-error slowing such that their performance was identical to that of healthy control subjects at baseline," the researchers wrote.
"The global burden of schizophrenia is greater than that of untreated AIDS, metastatic cancer or severe dementia," said Sohee Park, Gertrude Conaway Vanderbilt Professor of Psychology, who collaborated in the research. "The results of our study clearly indicate that it is possible to restore error-monitoring with tDCS."
In addition to measuring post-error slowing, the researchers measured how well the medial-frontal cortex communicated with another region of the frontal lobe called the lateral prefrontal cortex, which is also believed to play a role in adaptive control. Reinhart and his co-investigators found that this connection was abnormally reduced in people with schizophrenia compared to healthy people, but that again, stimulation improved the connection between the two regions equally well for both groups. This was another important finding, because it strongly suggests that this particular symptom of schizophrenia is not due to a categorical difference in the brain. Rather, it suggests that the schizophrenic brain is doing what a healthy brain does -- it's just not doing it as well.
This research has important implications for treatment. "Cognitive deficits in people with schizophrenia are treated with drugs, without significant success," Park said. "But I want to emphasize that there is much work to do before we can be certain that tDCS can be used as a treatment. We need to work out why and how these changes occur, how long these effects last and whether there are other consequences."
The researchers also caution that the tDCS systems used in research or the clinic shouldn't be confused with consumer devices that deliver electric current to the brain. "In the laboratory, tDCS is conducted in a controlled environment, and the safety of specific tDCS protocols are approved by institutional ethics review boards," Reinhart said. Home hobbyists should not try to replicate the research themselves.
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