Summary: New research challenges the longstanding belief that the striatum is involved in action selection. Instead of decision-making, the researchers found that the striatum and motor cortex work together to specify movement details, such as how they reach the object.
Using a new “hand-stringing” system, they recorded neural activity in mice and found that both areas were active during the execution of movement rather than decision-making. These findings can help reconstruct understanding of motor control and improve treatment of motor disorders such as Parkinson’s and Huntington’s disease.
Important facts
The role of striatum is reimagined: parameters of finely tuned movement of the striatum, not the choice of the striatum. Motor Cortex Collaboration: Both the striatum and motor cortex work together to specify the execution of movement. Infusion for Motion Disorders: Understanding the true role of the striatum may lead to better treatment of Parkinson’s disease and Huntington’s disease.
Source: HHMI
When you are weighing two possible actions, your brain needs to decide what to do and how to do it.
For example, if a book and cup are sitting side by side on a table, your brain must decide whether to read the novel or drink coffee. Also, your brain needs to know if it needs to reach 20 degrees in one way of the book or the other way of the cup to reach 20 degrees.
For decades, most neuroscientists have believed that one area of the brain, the basal ganglia, is the cause of the selection of action and another, the motor cortex, the specification of action.
Now using a new system developed in Janellia, researchers led by Dudman Lab have discovered that some of the basal ganglia, known as the striatum, are not involved in action selection as previously thought.
Instead, the striatum and motor cortex work together to specify movement parameters to carry out the action.
The new work sheds light on information that will help us better understand the role of the striatum in motor control, as well as movement disorders like Parkinson’s disease and Huntington.
“Now we can start thinking: how the striatum controls the speed of movement, how we can get it back online, how we can improve it,” says Josh Dudman, senior group leader at Janelia.
“A more accurate and conceptual model of how the striatum works will help you think more clearly about how to ultimately restore functionality.”
Design, build, test
The project began a decade ago when Dadman and his team began looking at data from the striatum that opposed existing models of the role of brain regions.
Their data were consistent with other observations on the striatum that questioned its traditional role. For example, this area is connected to the motor system and suggests that it may be involved in more mechanical aspects of behavior.
Furthermore, patients with motor disorders that affect the basal ganglia, such as Parkinson’s disease and Huntington, have no trouble deciding what they want to do, but have difficulty moving their limbs to do so.
The team sought to test the hypothesis that the striatum may be involved in a more mechanical aspect of flexible, goal-oriented actions.
To tear apart the various possibilities, researchers designed an experiment where the actions were roughly the same. Picking up a book involves slightly different movements than picking up a cup.
In this case, the patterns of neural activity are similar in specifications, but the selection is different. This allows researchers to distinguish between the two actions.
Researchers have worked with Janelia Experimental Technology to design a new “pull-to-” system that allows joysticks to be created in one of two slightly different positions that require roughly similar movement for access.
Researchers simultaneously recorded neural activity in both the striatum and motor cortex upon reaching the mouse, and then pulled a joystick to obtain a water reward. They found that neural activity in both brain regions was the same when animals reached and pulled onto the joystick at different locations.
These results suggest that both the striatum and motor cortex are involved in specifications rather than selection, and that animals cooperate to allow them to choose how to perform the action.
The team’s work raises questions about how these two brain regions coordinate to contribute to the same function. Rather than having multiple brain regions performing the exact same function as “too many cooks in the kitchen,” it seems likely that each region will contribute to subtle variations.
New findings suggest that behavior does not arise from a single agent, but is the result of many partial agents working together.
The study also details a novel system for testing hypotheses regarding the role of different brain regions in flexible, goal-oriented actions. This says the project the researchers say was empowered by Janellia.
“What we can say makes a big difference in our belief that we can build new experimental hardware that we need to run the experiments we have designed in a timely manner,” says Dudman.
“It’s not just speeding up that. It’s about going beyond the opportunity cost of the threshold and taking it before it falls below the opportunity cost of the threshold and really trying.”
About this neuroscience research news
Author: Nanci Bompey
Source: HHMI
Contact: Nanci Bompey – HHMI
Image: Image credited to Neuroscience News
Original research: Open access.
Josh Dudman et al. Neurons
Abstract
The binding specifications for neocortex and striatal actions.
The interaction between the two major forebrain structures, the cortex and the subcortical striatum, is important for flexible, goal-oriented actions.
Traditionally, it has been proposed that the primary motor cortex is involved in specifying continuous parameters of future/ongoing movements, while the striatum is important for selecting which type of action is initiated.
Recent data suggest that the striatum may also be involved in specifications. These alternatives were difficult to adjust because they made inherently indistinguishable predictions when comparing very clear actions, as often as they are.
Here we develop a quantitative model to reveal somewhat paradoxical insights. A strong distinction between predictions is made by simply comparing neural activity across similar actions. Therefore, we developed a new range-to-pull task where mice were reliably selected between two similar but different reach targets and pull forces.
The simultaneous cortical and subcortical recordings were uniquely consistent with the model in which the cortex and striatum co-specify the continuous parameters that manage movement performance.
