News in Science

'Mental map' key to navigation in the dark

Mammalian navigation We may be capable of navigating a familiar space in the dark without any sensory cues, such as sight, smell, touch and sound, says an Australian computational neuroscientist.

Dr Allen Cheung of the University of Queensland says research in animals suggests this is possible as long as we have a mental map of the space obtained from previous experience.

If confirmed by further experiments, Cheung's new theoretical analysis could have implications for understanding and helping navigation problems in people with dementia or vision impairment.

To model how the brain computes information for navigation, Cheung analysed data from studies that recorded the brain activity of lab rats as they moved around an enclosed space.

Such research has identified a number of important components of the mammalian navigation system, says Cheung.

These include gyroscope-like cells that measure the rotation of the head relative to the environment, GPS-like cells that indicate the animal's location in space, and a signal that tells whether the animal is moving forward or backwards.

In the dark

Previous research has shown that 'gyroscope cells' start to go off kilter and produce errors in navigation in the absence of visual cues from the environment.

Researchers have also assumed 'GPS cells' need visual cues to remain stable.

But, Cheung's theoretical analysis, published today in PLOS Computational Biology, suggests that under certain circumstances GPS cells can fire indefinitely, helping the animal to navigate, even in the dark.

"Not only does the animal not need visual cues, it doesn't need to know it has touched the side walls of the space, and it doesn't need to hear or smell or otherwise detect anything about the outside world," he says.

The findings hold as long as the animal has previously had an opportunity to use its senses to fully explore the boundaries of the area and develop a mental map of it, says Cheung.

After simulating navigation in many different shapes of enclosures, Cheung found the findings apply to shapes with 'one-fold rotational symmetry' -- a shape such as a kite that can only be superimposed on itself once it has been rotated 360°. Other enclosure shapes showed very little external input was also required, he says.

Cheung hopes to test his hypothesis in animals and humans in coming months.

It would be also interesting to test if the mental map remains key to navigation when an animal is not in the dark, he says.

"In the presence of visual cues the map may become less important."

And of course most animals in nature are in open spaces, not in the confined spaces that have been used to date to gather knowledge on mammalian navigation to date.

Helping navigation

Unfortunately, says Cheung, there are certain challenges studying animals in unconfined spaces, not least getting permission from an ethics committee.

Nonetheless, he says, there is evidence that humans have the same kind of navigation system as rats, and the new findings could contribute to our understanding of why people with dementia get lost.

"The region of the brain where these navigation cells are found is heavily implicated in the degeneration that occurs in all the dementias including Alzheimer's," says Cheung.

"This region is also part of a general memory system," he says.

The findings may also be useful in designing spaces that are easier to navigate for people who are vision impaired or have dementia, adds Cheung.

One theory is that people with dementia have difficulties processing a lot of sensory information.

Like people with vision impairment, they may benefit from houses that have a particular shape that needs minimal external input for navigation, he says.

"Although this, of course, is pure speculation."