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Researchers discover a new brain circuit, crucial for learning new motor skills

February 10, 2022 6:21 p.m. STI

Lisbon [Portugal], Feb 10 (ANI): Learning never ends. It is an integral part of growth. Likewise, learning new motor skills is an essential aspect of our lives. From playing the piano to riding a bike, it would be hard to imagine life without him. But how does the brain do it? A new study has shed light on a recently discovered brain circuit that may give us this remarkable ability.
The study was published in the scientific journal “Science Advances”.
The cortex forms the outer layer of our brain and is the ultimate multitasker, involved in everything from language and cognition to memory and voluntary actions. It is in fact, be used to read this very sentence by you. But it does not act alone and establishes extensive links with many other regions of the brain.
“We were particularly interested in two major types of cells in the cortex, the IT (intratelencephalic) and PT (pyramidal pathways) neurons”, specifies Nicolas Morgenstern, the first author of this study developed in the group at the time led by Rui Costa, at the Champalimaud Foundation, in Lisbon, Portugal.
“The IT and PT cells send signals from the cortex to another area buried deeper in the brain, called the striatum. These ‘cortico-striatal’ connections (i.e. the connections from the cortex to the striatum) are very important for motor learning and have been implicated in movement disorders like Parkinson’s disease.”
This is where the third major figure in the story appeared: the spiny projection neurons (SPNs), which made up 95% of the neurons in the striatum. The SPNs are directly contacted by the IT and PT cells. “We wanted to understand the different roles of IT and PT cells in this brain circuitry, which is so important for motor learning and behavior.”

To better understand these corticosteroid connections, the authors used a technique present in (almost) all the toolboxes of neuroscientists: optogenetics, a method of controlling cell activity using light. As Morgenstern explained, “We genetically engineered IT or PT cells in mice, allowing us to activate these cell types independently using optogenetics and measure their different effects on SPNs in the striatum. “.
Thanks to this approach, while recording the activity of neurons in vitro, the authors discovered a new corticostriate pathway. In this way, a fourth main player has emerged: striatal cholinergic interneurons (ChIs). Acting as a “middleman” in a three-person relay, ChIs in the striatum receive input from PT cells and, in turn, excite SPNs. “We found that PT cells preferentially connect to ChI, which indirectly activates SPNs,” Morgenstern said.
Using pharmacological methods, the authors were able to show precisely how ChI excites SPNs. When activated by PT neurons, ChIs release a neurotransmitter called acetylcholine (ACh). Neurotransmitters are chemical messengers that carry signals from one cell to another. When ChI releases ACh, it causes SPNs to be excited by nerve fibers of neighboring cells.
These results demonstrate that SPNs are excited twice: first, by the known direct pathways (IT-SPN and PT-SPN), and second, by this previously unknown indirect circuit (PT-ChI-SPN), which amplifies the initial excitement. What was the purpose of this double excitement? The authors hypothesized that the direct IT-SPN connection initially prepared specific motor actions, while the PT-ChI-SPN connection subsequently triggered movement.
“Apart from movement execution,” Nicolas Morgenstern noted, “this second excitatory phase mediated by PT neurons could be important for inducing long-lasting changes in the strength of specific connections, via the neurotransmitter ACh. behavior, since learning occurs when the connections between brain cells change”.
Therefore, in addition to making breakthroughs in the wiring of brain circuits that control movement and behavior, and helping us understand the different roles of IT and PT cells, this study may also provide us with an important piece in the puzzle. of how we learn.
“There’s still a lot to explore,” says the study’s lead author, Rui Costa, professor and director of the Zuckerman Mind Brain Behavior Institute, Columbia University. “For example, we are interested in understanding whether this circuit is affected in disorders like Parkinson’s disease or Huntington’s disease.” Although there is still a lot to discover, this study has made it possible to learn a little more about learning. (ANI)

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