[ad_1]
madison [US], Researchers have found that the human brain appears to be building a unique working model that works as predicted. The study revealed the importance of a specific type of connection between brain cells and may also explain ketamine’s promise as a treatment for depression.
This study is published in ‘The Journal of Neuroscience’. Researchers at the University of Wisconsin-Madison have demonstrated the top-down nature of this world view by disrupting it with small doses of an anesthetic drug called ketamine.
A bottom-up understanding of perception has prevailed for decades and states that sensory information moves from lower-order parts of the brain to “higher” parts that use it to perform executive functions such as focusing and planning. But the top-down approach has its roots in the 19th century. Now called predictive coding, the idea is that the frontal lobe of the brain makes predictions about what will happen next based on learned associations.
“You expect that if you hear a bark, you’ll see a dog,” said Sounak Mohanta, a graduate student in the lab of UW-Madison psychology and neuroscience professor Yuri Salmon.
“We used such associations to show how predictions affect behavior,” Mohanta said.
For their study, the researchers taught 32 volunteer associations that were completely new to them, playing them a three-letter nonsense word and following it with a picture from an assortment of unique animal-like shapes called grebles.
Through the feedback, the volunteers learned which sound was paired with which picture. The researchers then asked the volunteers to play a sound, show them a picture, and ask the volunteers to say whether the pair matched. The researchers mapped patterns in the brains of specific volunteers to correct sound-shape pairs by recording the electrical activity when the sound and shape appeared.
Once three of these associations were introduced, the predictive properties of the sounds were predicted by creating a paired grebel in the brains of test subjects 85 percent of the time, 50 percent of the time, or 33 percent of the time. . time.
“The stronger our listeners perceived a sound that was predicting a certain shape, the sooner they could tell us what shape we showed them,” Salmon said.
“Their reaction times were much slower for the 50-percent-predictive sounds, and still slower for the least-predictive sounds,” Salman said.
After hearing a highly predictive sound, activity in the subjects’ frontal lobes would increase, sending a signal to sensory centers in the back of the brain and activating brain cells, called neurons, that represent the expected size. Then, when the shape appears, those neurons become even more active and elicit a rapid response from the audience.
Unless the study subjects were administered ketamine.
“This drug, ketamine, blocked a whole set of processes, all one of those steps,” Mohanta said.
Neurons communicate by passing chemical signals across small gaps between neighboring cells. Each type of signal has a transmitter and a receptor. Ketamine interferes with a specific communication channel by blocking NDMA receptors, which are common on neurons along the pathway from the frontal lobe to sensory centers. This blocks the signal.
After a small dose of ketamine—prescribed by former UW-Madison anesthesiologist Rob Sanders, now at the University of Sydney in Australia—the highly predictive sound caused distinct, a lot of noise and disorganized activity in the frontal lobe. The pathway through the brain that normally prepared sensory centers for the anticipated size remained relatively quiet. Reaction times have been extended for all shapes, making them more like reaction times to less-predictable sounds.
“The priming signal is lost. The brain no longer benefits from top-down predictions, and errors occur,” said Salmon, whose work is supported by the National Institutes of Health.
Salmon said, “This experiment Sounak designed that whatever your idea of how perception comes together, you need to incorporate predictions into this feedback process as an important part of brain function.” “
Poor predictions are a feature of disorders including depression and schizophrenia, in that they may mislead someone that the worst is about to happen or may lead to hallucinations. Ketamine has been shown to relieve depression-like symptoms in animal studies, and is being used for clinical studies of depression.
“Blocking the negative predictors that are prominent in depressed patients may be how ketamine helps,” Salmon said.
First published:February 5, 2022, 8:39 pm
[ad_2]