From writing an article and typing to playing a violin or being a tennis star, the learning of tasks involving movement is one of the brain’s most complex challenges. How does one acquire new motor skills? Motor learning is an essential process by which the organism acquires skilled movements and the ability to associate new sensory information and actions, thus adapting to the ever-changing environmental demands of the world.
A new study at the Technion-Israel Institute of Technology in Haifa reveals how the brain reorganizes its neural networks during such skill learning and uncovers the vital role of dopamine in this process.
Published in prestigious journal Nature Communications under the title “VTA projections to M1 are essential for reorganization of layer 2-3 network dynamics underlying motor learning,” the study was led by Dr. Hadas Benisty, Prof. Jackie Schiller, and medical doctoral student Amir Ghanayim, with contributions from Prof. Ronen Talmon and student Avigail Cohen-Rimon from the Technion’s Andrew and Erna Viterbi Faculty of Electrical and Computer Engineering.
They found that the local release of dopamine – a molecule best known for its role in the brain’s reward system – is a key factor in acquiring new motor skills. Such an ability is always needed for adapting to our environment. This learning takes place in the primary motor cortex – a region of the brain responsible for planning and executing voluntary movements. From this cortical “command center,” signals are sent via the spinal cord to activate muscles and coordinate movement. Neural activity in this region is known to change as we learn new skills, but the mechanisms that drive these changes have remained unclear.
The researchers used advanced chemical and genetic techniques to temporarily switch off targeted brain cells, allowing researchers to study their function. They used a control group whose heads were attached to a device for some 40 minutes but they did nothing more to them. The group that was tested (not a control group) was of “behaved mice” – as scientists refer to the mice – whose heads are held stable by gluing something to their heads, for about 40 minutes. They are not hurt, and after the experiment, they are freed.
The scientists wanted the mice to reach for, grasp and eat a food pellet with their forelimbs.
The control animal group demonstrated a steady and gradual improvement in motor execution of the task until reaching a stable level.
Those mice that were not in the control group went under the microscope were trained to perform a head-fixed version of the forelimb grasping task, where mice learn to reach for, grab, and eat a food pellet, the researchers said. They mapped dynamic changes in neural networks with cellular resolution within the motor cortex during the acquisition of a motor skill and discovered that during learning, neural networks transition from a “beginner” to an “expert” structure.
Release of dopamine in the motor cortex
Crucially, this process depends on the local release of dopamine in the motor cortex. Under normal conditions, dopamine molecules are brought to this region by neurons originating in the ventral tegmental area (VTA) – a central dopamine hub in the brain. The researchers hypothesized that this dopamine release triggers plasticity mechanisms, leading to changes in functional connectivity among neurons in the motor cortex. This process enables motor learning by storing new skills for future use. In essence, this is a form of reinforcement learning, where successful movement outcomes reinforce the brain’s internal wiring.
To test the necessity of this mechanism, the researchers examined both the activity and functional connectivity of the neural network and the learning process when dopamine release in the primary motor area was blocked.
The results were clear: When dopamine was blocked, learning stopped completely – mice were unable to improve their performance in a task to extend their forelimbs. The motor cortex neural network remained static but as soon as dopamine release was restored, learning resumed, along with reorganization of the neural network.
The results are important because they provide compelling evidence that the local release of dopamine serves as a crucial signal for neural plasticity in the motor cortex, enabling the necessary adaptations for producing precise and efficient motor commands. A particularly interesting discovery was that blocking dopamine did not affect previously learned motor skills – the team proved that dopamine is essential for learning new movements but is not needed for performing those that have already been learned.
“In general, if we learn how the brain learns, it could help people who have difficulty learning, or motor problems, neurological,” Benisty told The Jerusalem Post. “If you don’t know how something works, you won’t know how to fix it.”
She concluded, “Our work is another step toward understanding brain plasticity and learning mechanisms at the cellular and network levels and highlights the brain’s ability to reorganize itself, allowing us to refine our motor skills throughout life. These insights could also have important implications for treating neurological disorders such as Parkinson’s disease, in which dopamine production is impaired and motor learning is compromised.