Researchers have gained new understanding of how the brain controls movement using both overt motor control and brain-machine interface (BMI) control.
Their findings provide insight into the distinct neural processes involved in BMI control compared to natural movement.
Key Facts:
- Rhesus monkeys were trained to control a cursor using either overt arm movements or a BMI that decoded motor cortical activity.
- Local field potentials were recorded from motor cortex, prefrontal cortex, and striatum during both types of control.
- Prefrontal cortex activity best distinguished BMI and overt motor control during movement planning.
- Motor cortical activity best distinguished control types during movement execution.
- Information flowed from prefrontal cortex to motor cortex during both control types.
- Information flowed from striatum to motor cortex during BMI control.
Source: bioRxiv 2023
Prefrontal Cortex Key for Planning, Motor Cortex for Execution
Scientists have developed remarkable BMI systems that allow paralyzed patients to control computer cursors or robotic limbs just by thinking.
However, we still don’t fully understand how the brain adapts to outputting motor commands via a BMI compared to natural movement.
Researchers at UC Berkeley took a big step toward unraveling these neural processes.
They trained rhesus monkeys to perform a 2D center-out reaching task using either overt arm movements or a BMI controlled by their motor cortical activity.
Importantly, while the monkeys performed the tasks, the team simultaneously recorded neural activity from three brain regions: the motor cortex, prefrontal cortex, and striatum.
This allowed them to compare the activity patterns between overt motor control and BMI control.
Their findings suggest that the prefrontal cortex holds distinct representations of overt and BMI control during movement planning.
In contrast, the motor cortex is most distinct between control types during movement execution.
Planning vs. Execution: Center-Out Task
In the center-out task, the monkey had to hold at a center target before getting a cue to move to one of eight peripheral targets.
This “go cue” can be thought of as the planning phase, when the monkey selects the upcoming movement trajectory.
The period near target acquisition is more focused on precise execution.
The researchers found that prefrontal cortex activity right after the go cue best distinguished between overt motor and BMI control.
Meanwhile, motor cortical activity right before reaching the peripheral target was most predictive of control type.
This aligns well with what we know about these brain regions’ functions.
The prefrontal cortex is important for high-level functions like action selection, planning, and decision-making.
The motor cortex directly controls movement execution.
Results suggest that the prefrontal cortex plays an important upstream role in both BMI and overt motor control tasks, with especially distinct representations during movement planning.
Information Flow in the Brain: Between Regions
Analyzing directed interactions between brain regions provided further insight.
The researchers found that information flowed from the prefrontal cortex to the motor cortex during both overt and BMI control.
This highlights the prefrontal cortex’s role in sending planning and initiation signals.
Additionally, they observed information flow from the striatum to motor cortex specifically during BMI control.
The striatum is important for learning new motor skills, so this connectivity may facilitate learning to output motor commands through a BMI.
Implications for Brain-Machine Interface (BMI) Development
These findings help paint a picture of how the brain adapts to outputting motor commands via a BMI decoder versus natural movement.
This has important implications for the development of BMIs to help paralyzed patients.
The fact that prefrontal activity was particularly distinct between control types during planning highlights that BMI control requires different high-level cognitive processes.
Patients need to learn to initiate movements by modulating their neurons instead of just willing an arm movement.
Understanding these neural mechanisms will help researchers design training protocols and decoders that facilitate this adaptation.
Identifying specific brain regions like the prefrontal cortex and striatum that contribute to BMI control also opens the door for new decoding approaches.
Authors stated: “Our results contribute to a growing body of work elucidating the neural mechanisms underlying BMI control, improving our understanding of BMIs as a scientific tool and as a therapeutic device.”
Unlocking the distinct neural processes behind overt motor control versus BMI control will ultimately help optimize these systems to better serve patients.
This study provides key insights that bring us steps closer.
References
- Study: Distinct neural representations during a brain-machine interface and manual reaching task in motor cortex, prefrontal cortex, and striatum
- Authors: Ellen L. Zippi et al. (2023)
