Summary: Mental maps in the brain are activated when we think about sequences of experiences, even without physical movement. In an animal study, they found that the entorhinal cortex contains a cognitive map of experiences, which is activated during mental simulation.
This is the first study to show the cellular basis of mental simulation in a non-spatial domain. The findings could improve our understanding of brain function and memory formation.
Key facts:
- Mind maps are created and activated without physical movement.
- The entorhinal cortex holds cognitive maps of experiences.
- This study provides insights into the cellular basis of mental simulation.
Source: myth
As you travel your usual route to work or the grocery store, your brain engages the cognitive maps stored in your hippocampus and entorhinal cortex. These maps store information about the paths you’ve taken and the locations you’ve been to before, so you can navigate whenever you go there.
New research from MIT has found that such mental maps are also created and activated when you simply think about sequences of experiences, in the absence of any physical movement or sensory input.
In an animal study, researchers found that the entorhinal cortex contains a cognitive map of what animals experience as they use a joystick to scroll through a sequence of images. These cognitive maps are then activated when we think about these sequences, even when the images are not visible.
This is the first study to show the cellular basis of mental simulation and imagination in a nonspatial domain through the activation of a cognitive map in the entorhinal cortex.
“These cognitive maps are being recruited to perform mental navigation, without any sensory input or motor output. We are able to see a signature of this map being introduced as the animal is mentally going through these experiences,” says Mehrdad Jazayeri, an associate professor of brain and cognitive sciences, a member of MIT’s McGovern Institute for Brain Research, and author old. of study.
McGovern Institute Research Scientist Sujaya Neupane is lead author of the paper, which will appear in Nature. Ila Fiete, professor of brain and cognitive sciences at MIT, member of MIT’s McGovern Institute for Brain Research, director of the K. Lisa Yang Integrative Computational Neuroscience Center, is also an author of the paper.
Mind maps
A great deal of work in animal models and humans has shown that representations of physical locations are stored in the hippocampus, a small seahorse-shaped structure, and the nearby entorhinal cortex. These representations are activated whenever an animal moves through a space it has been in before, just before traversing the space, or when it is asleep.
“Most previous studies have focused on how these areas reflect the structures and details of the environment as an animal physically moves through space,” says Jazayeri.
“When an animal moves around a room, its sensory experiences are well encoded by the activity of neurons in the hippocampus and entorhinal cortex.”
In the new study, Jazayeri and his colleagues wanted to explore whether these cognitive maps are built and then used during purely mental transitions or imagining movement across non-spatial domains.
To explore this possibility, researchers trained animals to use a joystick to trace a path through a sequence of images (“landmarks”) spaced at regular time intervals. During training, animals were shown only a subset of image pairs, but not all pairs. After the animals had learned to navigate through the training pairs, the researchers tested whether the animals could cope with new pairs they had never seen before.
One possibility is that animals do not learn a cognitive map of the sequence, and instead solve the task using a memorization strategy. If so, it is expected that they will fight with the new couples. Instead, if animals were to rely on a cognitive map, they should be able to generalize their knowledge to new pairs.
“The results were inconclusive,” says Jazayeri. “The animals were able to mentally navigate between new pairs of images from the first time they were tested. This finding provided strong behavioral evidence for the presence of a cognitive map. But how does the brain create such a map?”
To address this question, the researchers recorded from single neurons in the entorhinal cortex while the animals performed this task.
The neural responses had a striking feature: as the animals used the joystick to navigate between two landmarks, the neurons displayed distinct spikes of activity associated with the mental representation of the intervening landmarks.
“The brain goes through these spikes of activity at the expected time when the intrusive images would have passed the animal’s eyes, which they never did,” says Jazayeri.
“And the time between these bumps, critically, was exactly the time the animal would expect to reach each one, which in this case was 0.65 seconds.”
The researchers also showed that the speed of mental simulation was related to the animals’ performance on the task: When they were slightly late or early in completing the task, their brain activity showed a corresponding difference in time.
The researchers also found evidence that mental representations in the entorhinal cortex do not encode specific visual features of images, but rather the ordinal arrangement of landmarks.
A learning model
To further explore how these cognitive maps might work, the researchers built a computational model to mimic the brain activity they found and demonstrate how it could be generated.
They used a type of model known as a continuous attractor model, which was originally developed to model how the entorhinal cortex tracks the position of an animal as it moves, based on sensory input.
The researchers customized the model by adding a component that was able to learn activity patterns generated by sensory input. This model was then able to learn to use those patterns to reconstruct those experiences later, when no sensory input was available.
“The key element we had to add is that this system has the capacity to learn bidirectionally by communicating with sensory input. Through the associative learning that the model goes through, it will actually recreate those sensory experiences,” says Jazayeri.
The researchers now plan to investigate what happens in the brain if the landmarks are not evenly spaced, or if they are arranged in a ring. They also hope to record brain activity in the hippocampus and entorhinal cortex as the animals first learn to perform the navigation task.
“Seeing the memory of the structure that crystallizes in the mind and how that leads to the neural activity that emerges is a really valuable way to ask how learning happens,” says Jazayeri.
Funding: The research was funded by the Natural Sciences and Engineering Research Council of Canada, the Québec Research Funds, the National Institutes of Health and the Paul and Lilah Newton Brain Science Award.
About this memory search news
Author: Abby Abazorius
Source: myth
Contact: Abby Abazorius – MYTH
Image: Image is credited to Neuroscience News
Original research: Closed access.
“Vector production via mental navigation in the entorhinal cortex” by Mehrdad Jazayeri et al. Nature
ABSTRACT
Vector production via mental navigation in the entorhinal cortex
A cognitive map is a suitably structured representation that enables new computations using prior experience; for example, planning a new route in a known space. Work in mammals has found direct evidence for such representations in the presence of exogenous sensory input in both spatial and non-spatial domains.
Here we tested a fundamental postulate of the original cognitive map theory: that cognitive maps support endogenous computations without external input.
We recorded from the entorhinal cortex of monkeys in a mental navigation task that required the monkeys to use a joystick to produce one-dimensional vectors between pairs of visual points without seeing the intervening landmarks.
The monkeys’ ability to perform the task and generalize to novel pairs indicated that they relied on a structured representation of landmarks. Task-modulated neurons exhibited periodicity and spiking that matched the temporal structure of landmarks and showed signatures of persistent attractor networks.
A persistent attractor network model of path integration augmented with a Hebbian-like learning mechanism provided an explanation of how the system could endogenously remember landmarks.
The model also made the unexpected prediction that endogenous landmarks temporarily slow path integration, restore dynamics, and thereby reduce variability. This prediction was confirmed in a reanalysis of firing rate variability and behavior.
Our findings link structured patterns of activity in the entorhinal cortex to the endogenous recruitment of a cognitive map during mental navigation.
