nature neuroscience (2022). DOI: 10.1038/s41593-022-01194-3″ width=”685″ height=”342″/> A paradigm to study long-term neuronal and behavioral stability. Credit: Nature Neuroscience (2022). DOI: 10.1038/s41593-022-01194 -3
While many studies have explored the fundamentals of the mammalian motor system (i.e., the collection of neural networks that enable mammals to move in specific ways), some questions remain unanswered. One of these questions concerns how recurring or stable behaviors are maintained in the brain.
Some theories and research suggest that the neural activity underlying stable behaviors is itself very stable. However, others have suggested the possibility that the activity of individual motor neurons could change significantly over time, despite similar behavioral patterns.
Harvard University researchers recently attempted to approach the solution to this long-standing debate by observing rodent behavior and neural activity. Their results, published in Nature Neuroscience, suggest that the activity of individual neurons in brain regions associated with movement and physical behavior patterns is very stable over time.
“Stability at the level of individual neurons is not required in a highly degenerated system like the brain, where many different activity patterns can perform the same work,” Bence P. Ölveczky, one of the researchers who conducted the study, told MedicalXpress. “The notion that neural representations of behavior drift in output-invariant subspaces is widely accepted. But is that so, or has the brain found a way to stabilize activity at the level of individual neurons?”
To test their hypothesis, the researchers had to record their rodents’ brain activity over long periods of time, as they exhibited very stable behaviors. Ölveczky’s lab routinely trains rats to produce complex “dances,” or patterns of behavior that, once learned, are very stable. Therefore, the team simply records the activity of individual motor-related neurons over long periods of time while the rats exhibit these stable behaviors.
“We have developed a system that enables us to record the same neurons continuously for weeks,” explains Ölveczky. “To eliminate any source of variability that could confound our experiments, our animals performed the same behavior at the same time of day in the same box under the same conditions for weeks. The results were striking: the neural activity patterns of individual neurons were super stable over weeks of recording, reflecting the stability of the behavior itself.”
In order for their results to be reliable, Ölveczky and his colleagues had to study very stable and stereotyped behavior consisting of specific movement patterns that can be measured very precisely. They taught the rats to complete a simple task in which they were rewarded for pressing a lever in a precisely timed order.
Over time, their rats learned intricate and idiosyncratic movement patterns that eventually allowed them to complete the task and receive their water reward. These patterns could be likened to the stable movement patterns that humans can learn throughout their lives, such as serving in tennis or volleyball.
“We found that the patterns learned by our rats became very stable over months, and we recorded the activity of the same cells over weeks under very regimented conditions, as explained above,” Ölveczky said. “We also used an innate behavior, wet dog shaking, which is highly stereotyped and the structure of which we can accurately measure. I think our study answers an important question about how stable behaviors and memories are maintained.”
Overall, recent work by Ölveczky and his colleagues suggests that the brain maintains stable and consistent behaviors by “freezing” the activity patterns of individual neurons. This is consistent with the clear idea, suggested by previous work, that neural activity can drift around as long as its projections onto relevant control units (so-called “output units”) are stable.
“While our work establishes the phenomenon of stability of individual neurons in stable behavior, it remains a mystery how such patterns of activity are maintained in circuits that are constantly being reshaped by new experiences and other processes,” added Ölveczky. “Ensuring such stability will likely require an active process, which we would like to understand. We would also like to challenge the animals that maintain stable behaviors to learn other similar behaviors using the same neural circuits, and then investigate whether such ‘multitasking’ leads to instabilities and interference between behaviors .”
More information:
Kristopher T. Jensen et al., Long-term stability of the activity of individual neurons in the motor system, Nature Neuroscience (2022). DOI: 10.1038/s41593-022-01194-3
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Citation: Rodent study shows single motor neuron activity is stable over time (2022, November 28) retrieved December 1, 2022 from https://medicalxpress.com/news/2022-11-rodents-motor- neurons-stable.html
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