Scientists have identified a “dial” in the human brain that increases when exploring new areas. The discovery could help understand why getting lost is often an early symptom of dementia such as Alzheimer’s disease.
Imagine you are walking home along a well-worn road and accidentally take the wrong turn. It doesn’t take long for your brain to sound the alarm that you’ve lost your way.
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“When you move to a new city or travel somewhere, you don’t fit in right away,” study co-author Deniz Vatancevar, a neuroscientist at Fudan University in China, told Live Science. “You need to explore your environment in order to become familiar with it.” Vatansever and his team aimed to recreate this experience in VR.
They recruited 56 healthy volunteers between the ages of 20 and 37, each of whom navigated a virtual world inside the scanner. They explored a virtual environment (a grassland surrounded by mountains) while looking for six “items” hidden within it. Vatansever’s team used functional MRI, a technique that tracks blood flow in the brain, to monitor the volunteers’ brain activity as they explored familiar and unknown areas of the world.
The research team zoomed in on the hippocampus, a brain region important for memory and navigation. The seahorse-shaped hippocampus is rich in place cells that light up in response to specific locations. Previous research has shown that there are cells in one end of the hippocampus that fire when people think about location in broader terms, such as where landmarks in a nearby city are. At the other end, place cells are activated when you think about a specific place, such as where you keep your cereal box in the kitchen.
Between the “head” and “tail” of the hippocampal seahorse, there is a gradient of activity that connects these broad and finely tuned positional representations. But no one had previously investigated the organization of cells that respond to the novelty and familiarity of a place.
Vatansever’s team discovered that there are cells in the head of the hippocampus that fire when participants explore areas they were previously in. Cells in the tail responded to the new position. And the entire region was arranged in a gradation from familiar to unfamiliar.
“As you go from one end to the other, you see the level of novelty and familiarity change,” Batanseva says.
Jita Patai, a cognitive neuroscientist at University College London who was not involved in the study, said previous studies have yielded mixed results about which areas of the hippocampus respond to environmental novelty or familiarity. “What they show is that [the discrepancy] That may be partly due to the fact that it’s a gradient,” she told Live Science.
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Other brain regions also responded differently to new and familiar locations. There was a cone-shaped gradient in the area of the cortex, the brain’s high-level thinking center. “At the heart of it is a part of us that ‘likes’ more familiarity, and as we move away from that, we increasingly prefer novelty-seeking and aggressive behavior,” Vatansever said.
The researchers also investigated whether moving between familiar and unfamiliar areas activated broader brain networks, or groups of cells that were spread throughout the brain and often activated in synchrony. Familiar regions activated networks previously associated with motor control and memory, whereas new regions activated networks associated with concentration and perception.
This division may help the brain adapt to new environments by focusing on and absorbing relevant details, Vatancevar said. And he proposed that a combination of memory and motor control helps us navigate familiar territory.
This finding may explain some of the early signs of dementia, Professor Batansevaa suggested. Cells within the cortical and hippocampal gradients happen to be one of the first brain regions affected by Alzheimer’s disease. In the early stages of the disease, both the anterior and posterior regions of the hippocampus are equally vulnerable.
Louis Renaud, a cognitive neuroscientist at the University of East Anglia who was not involved in the study, said the paper shows a strong link between navigation and memory.
The areas of the brain that help us navigate are also key to episodic memory, which relates to specific events in our lives rather than factual knowledge, Renaud told Live Science. Episodic memory is also particularly vulnerable in the early stages of Alzheimer’s disease.
A better understanding of how navigation is encoded in the brain could reveal measurable signs of the early stages of dementia, when navigational abilities begin to decline.
“If you want people to be more independent, you want to be able to go to new places and understand new things,” Patai says. “In that sense, the connection between spatial novelty and memory is very interesting.”
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