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Dopamine and serotonin are brain chemicals that affect a range of neurological disorders, including Parkinson's disease and depression, so understanding how they work could be key to developing more effective treatments for these conditions.

The new tool offers an unprecedented look at these neurotransmitters in action, allowing scientists to track their activity in real time for the first time.

Both dopamine and serotonin have long been linked to the brain's ability to process rewards, but more recently, scientists are drawing attention to the fact that they may play a more important role in the human body. This varies from how serotonin in the gut can regulate blood sugar levels or how low levels can be eliminated with ketamine, and how deep brain stimulation (DBS) can boost dopamine production in patients with Parkinson's disease.

The latter example is particularly promising, since Parkinson's disease is characterized by depletion of dopamine production in the brain, which leads to loss of control over body movements. Using DBS, in which a patient is implanted with tiny wires to deliver electrical current to specific areas of the brain, is a way to address symptoms such as tremors and slow movement, as well as dopamine deficiency.

Five patients had to undergo DBS treatment, two with Parkinson's disease and three with essential tremor, an involuntary motor disorder of the nervous system.

When a neurosurgeon implanted electrode arrays for DBS therapy, another group of scientists worked with them to insert their own carbon-fiber microelectrode deep into the brain, which was designed to detect and register serotonin and dopamine as they are released from neurons.

While the patients were awake, the researchers asked them to perform some decision-making exercises in which they had to decide which direction a series of dots moved across the screen after they disappeared. Each patient completed the task 200 to 300 times, and sometimes they were asked to indicate how confident they were in their answers.

Meanwhile, low voltages were applied to the electrode to determine the activity of dopamine and serotonin in real time. Scientists call this electrochemical method cyclic voltammetry with fast scanning, and it allowed them to register for the first time subsecond fluctuations in the transmission of dopamine and serotonin signals.

"A huge number of people around the world take pharmaceutical drugs, which can disrupt the dopamine and serotonin transmission systems and change behavior and mental health," p said. Reed Montague of Virginia Tech, senior author of the study.

"For the first time, the current activity of these systems was measured, and it was determined that it affects perception and cognitive abilities. These neurotransmitters simultaneously act and integrate activity at completely different time and spatial scales than anyone previously expected."

The scientists were able to draw some useful conclusions from their experiments.

They found that serotonin levels rose when the subject was more unsure of their response, and fell when they were more confident. Dopamine appeared to increase as subjects waited for their decisions to be made, while serotonin levels dropped, and finally, when the choice was made, both reached a certain level.

"This study sheds light on the role of these neurochemicals in learning, brain plasticity, and our perception of the environment," said principal investigator Kenneth T. Kishida.

"We now have a more detailed understanding of how our brains shape what we perceive, use that perception to make decisions, and interpret the consequences of the choices we make. Dopamine and serotonin seem to be crucial in all these processes. Importantly, research like this will help us and other scientists better understand how medications such as serotonin reuptake inhibitors affect cognitive abilities, decision-making, and affect mental States such as depression."

The study was published in the journal Neuron.

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