summary: New research reveals how the brain forms a cohesive mental map of space and highlights the critical role of sleep in this process. “Place cells” in the hippocampus mark specific locations, while weaker spatial cells stitch these points together into a comprehensive cognitive map.
The researchers observed that sleep refines these maps, allowing the brain to connect locations and encode them into mental geography. This finding highlights the importance of both subtle neural activity and rest in enhancing our ability to navigate and plan our environment.
Important facts:
- Weak spatial cell: These cells connect memories of discrete locations into mental maps and are essential for navigation.
- Role of sleep: Sleep refines and strengthens neural connections and enhances cognitive mapping.
- Cognitive map: These maps provide a schematic representation of space, allowing for mental exploration and planning.
sauce: MIT Picower Institute
On the first day of your vacation in a new city, you can get to know countless individual places through exploration. It feels like the memories of these spots (beautiful gardens on quiet side streets, etc.) won’t fade any time soon, but they’re still strong enough to draw new tourists to the same places, and even to the cafes you found. It may take a few days to get a feel for the neighborhood nearby.
A new study in mice by neuroscientists at the Massachusetts Institute of Technology’s Picower Institute for Learning and Memory provides new evidence of how the brain forms cohesive cognitive maps of entire spaces, and the This highlighted the extreme importance of sleep.
Scientists have known for decades that the brain uses neurons in an area called the hippocampus to remember specific locations. So-called “place cells” are activated reliably when an animal is in a location that neurons have been conditioned to remember.
But rather than having specific spatial markers, it’s more useful to have a mental model of how they’re all related within a continuum of overall geography.
Although such “cognitive maps” were formally theorized in 1948, neuroscientists remain unclear about how the brain constructs them.
New research in December issue cell report This ability relies on subtle but meaningful changes over several days in the activity of cells that are only weakly tuned to individual locations but increase the robustness and sophistication of hippocampal encoding across space. I discovered that there may be.
Analysis of the study shows that with sleep, these “spatially weak” cells increasingly enhance neural network activity in the hippocampus, linking these locations into cognitive maps.
“On day one, the brain doesn’t represent space very well,” says Sherman Fairchild Professor in the Picower Institute and Massachusetts Institute of Technology’s Department of Biological and Brain Sciences and a researcher in the lab of lead author Matthew Wilson. said lead author Wei Guo. Cognitive science.
“Neurons represent individual locations, but they don’t work together to form a map. But on day five they form a map. If you want a map, all these neurons work together. and work as an ensemble.”
mouse mapping maze
To conduct the study, Guo and Wilson, along with labmates Jie “Jack” Zhang and Jonathan Newman, introduced mice to simple mazes of various shapes, and used them for several days, with approximately We were given 30 minutes to explore freely. Importantly, the mice were not instructed to learn anything specific by providing a reward.
They just wandered. Previous studies have shown that mice spontaneously exhibit spatial “implicit learning” several days after this type of unrewarding experience.
To understand how implicit learning becomes entrenched, Guo et al. They visually monitored hundreds of neurons.
They recorded flashes of neurons not only when the mice were actively exploring, but also when they were asleep. Wilson’s lab has shown that animals refine their memories by “replaying” previous journeys during sleep, essentially dreaming about their experiences.
Analysis of the recordings showed that place cell activity developed instantly and remained strong and unchanged over several days of exploration. However, this activity alone cannot explain how latent learning and cognitive maps evolve over a few days.
So unlike many other studies in which scientists focus only on the strong, distinct activity of place cells, Guo believes that the more subtle and mysterious activity of cells that are not so strongly tuned spatially We extended the analysis to activities.
Using a new technique called “manifold learning,” he discovered that many of the “spatially weak” cells gradually correlate their activity not with location, but with patterns of activity among other neurons in the network. I was able to identify that.
While this was happening, Guo’s analysis showed that the network encoded a cognitive map of the maze that increasingly resembled a literal physical space.
“While cells with strong spatiality do not respond to specific locations like cells with strong spatiality, cells with weak spatiality are specialized in responding to “mental locations,” or specific ensemble firing patterns of other cells. ” wrote the study authors.
“If the mental domain of a weak spatial cell encompasses two subsets of strong spatial cells that encode different locations, this weak spatial cell can act as a bridge between these locations.”
In other words, weak spatial cell activity may piece together individual locations represented by place cells into a mental map.
need for sleep
Research from Wilson’s lab and many others has shown that memories are consolidated, refined, and processed through neural activity, including replay, that occurs during sleep and rest.
Guo and Wilson’s team therefore sought to test whether sleep is required for the contribution of weak spatial cells to the implicit learning of cognitive maps.
To do this, they had several mice explore a new maze on the same day, separated by three-hour naps. Some mice were put to sleep, while others were not. Those who were allowed to sleep showed significant improvements in their mental maps, while those who were not allowed to sleep showed no such improvement.
Not only has the map’s network encoding been improved, but measurements of individual cell coordination during sleep show that cells are more sensitive to both the location and pattern of network activity, so-called “mental locations” or “fields.” It has been shown to help you become better attuned.
Meaning of mental map
Guo points out that the “cognitive map” that the mice encoded over several days was not a literal, accurate map of the maze. Rather, they resembled schematics. Their value is that they provide the brain with a topology that can be mentally explored without being in physical space.
For example, once you’ve created a cognitive map of your hotel’s surroundings, you can plan an excursion for the next morning (e.g., pick up a croissant at the bakery a few blocks west, then eat it at the next location. You can imagine) that bench you saw in the park by the river).
In fact, Wilson hypothesized that weak spatial cell activity may superimpose salient non-spatial information that gives the map additional meaning (i.e., the concept of a bakery, even if (not spatially, even though it is closely related to the location of). However, this study did not include landmarks within the maze, nor did it test specific behaviors between mice.
However, since this study found that cells with weak spatial awareness contribute meaningfully to map creation, future research will investigate what kind of information these cells incorporate into animals’ sense of the environment. Wilson said they could investigate. Intuitively, we seem to see the space we live in as more than just a collection of individual places.
“In this study, we focused on the animals’ natural behavior and demonstrated that during free-exploration behavior and subsequent sleep, substantial neuroplastic changes at the ensemble level still occur even in the absence of reinforcement. ” concluded the authors.
“This form of implicit and unsupervised learning constitutes an important aspect of human learning and intelligence and requires further investigation.”
Funding: The Freedom Together Foundation, the Picower Institute for Learning and Memory, and the National Institutes of Health funded the study.
About this sleep and neuroscience research news
author: david orenstein
sauce: MIT Picower Institute
contact: David Orenstein – MIT Picower Institute
image: Image credited to Neuroscience News
Original research: Open access.
“Latent learning drives sleep-dependent plasticity in different CA1 subpopulationsWritten by Matthew Wilson et al. cell report
abstract
Latent learning drives sleep-dependent plasticity in different CA1 subpopulations
Implicit learning is a process that allows the brain to convert experience into a “cognitive map,” a type of implicit memory, without the need for reinforcement training.
To investigate the neural mechanism, we recorded from mouse hippocampal neurons during latent learning of a spatial map and observed that the high-dimensional neural state space gradually transformed into a low-dimensional manifold that closely resembles the physical environment. .
This conversion process is associated with the neural reactivation of navigational experiences during sleep.
Furthermore, we identified a subset of hippocampal neurons that, rather than forming place fields in novel environments, maintain weak spatial tuning but gradually develop activity that correlates with other neurons.
The improved correlation introduces redundancy into the ensemble code, transforming the neural state space into a low-dimensional manifold, effectively linking the discrete location fields of the location cells into a map-like structure.
These results suggest a potential learning mechanism for spatial maps in the hippocampus.
