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06-16-2024

Mental maps help the brain remember places and paths

Mental maps play a crucial role as you navigate your daily route to work or the grocery store.

These cognitive maps, stored in your hippocampus and entorhinal cortex, retain information about paths you’ve taken and locations you’ve visited, enabling you to find your way effortlessly. But what happens when you only think about a location?

New research has uncovered that these mental maps are not just for physical navigation. Even thinking about sequences of experiences can activate these cognitive maps, revealing a fascinating aspect of how our brains work.

Cognitive map

A remarkable study conducted by researchers at MIT has found that mental maps are created and activated purely by thought, without any physical movement or sensory input.

In this animal study, researchers discovered that the entorhinal cortex stores a cognitive map of sequences experienced while using a joystick to browse through images.

Remarkably, these maps are activated when thinking about the sequences, even without seeing the images.

Mehrdad Jazayeri is an associate professor of brain and cognitive sciences, a member of MIT’s McGovern Institute for Brain Research, and the senior author of the study.

“This is the first study to show the cellular basis of mental simulation and imagination in a nonspatial domain through activation of a cognitive map in the entorhinal cortex,” said Jazayeri.

Mental maps: Beyond physical spaces

Previous studies have shown that representations of physical locations are stored in the hippocampus and entorhinal cortex, activated when an animal moves through a familiar space or even when it is asleep.

“Most prior studies have focused on how these areas reflect the structures and details of the environment as an animal moves physically through space,” explained Jazayeri.

In their new study, the researchers explored whether cognitive maps are built and used during purely mental run-throughs or imagination.

They trained animals to use a joystick to navigate through a sequence of images spaced at regular intervals.

Initially, the animals were shown only subsets of image pairs. Once trained, they were tested with new pairs they had never seen before.

Evidence of mental maps

The results were clear. The animals could mentally navigate between new image pairs from the first test, demonstrating strong behavioral evidence for cognitive maps.

“This finding provided strong behavioral evidence for the presence of a cognitive map. But how does the brain establish such a map?” noted Jazayeri.

To investigate, the researchers recorded neural responses in the entorhinal cortex as animals performed the task. They found distinctive activity patterns, or “bumps,” representing the mental navigation through images.

“The brain goes through these bumps of activity at the expected time when the intervening images would have passed by the animal’s eyes, which they never did,” explained Jazayeri.

Speed of thought

The researchers also noted that the speed of mental simulation was related to the animals’ task performance.

When the animals were early or late in completing the task, their brain activity timing showed corresponding changes.

Additionally, the mental representations in the entorhinal cortex encoded the order of the landmarks, not their visual features.

Modeling the mind

To further understand these mental maps, the researchers developed a computational model mimicking brain activity. They used a continuous attractor model, originally designed to track an animal’s position based on sensory input.

By adding a component for learning activity patterns from sensory input, the model could reconstruct experiences without sensory input.

“The key element we needed to add is that this system has the capacity to learn bidirectionally by communicating with sensory inputs. Through associational learning, the model recreates those sensory experiences,” said Jazayeri.

The intricacies of learning and brain activity

The researchers plan to explore what happens if the landmarks are unevenly spaced or arranged differently. They also aim to record brain activity as animals first learn the navigation task.

“Seeing the memory of the structure become crystallized in the mind, and how that leads to neural activity, is a valuable way of understanding how learning happens,” concluded Jazayeri.

The research opens new avenues for understanding how our brains navigate not just the physical world but also the complex landscapes of our thoughts and experiences.

The study is published in the journal Nature.

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