It might be cheesy, but this mouse has a 6th sense (Image: Will & Deni McIntyre/SPL)

Who needs sight to get around when you’ve got a digital compass in your head? A neuroprosthesis that feeds geomagnetic signals into the brains of blind rats has enabled them to navigate around a maze.

The results demonstrate that the rats could rapidly learn to deploy a completely unnatural “sense”. It raises the possibility that humans could do the same, potentially opening up new ways to treat blindness, or even to provide healthy people with extra senses.

“I’m dreaming that humans can expand their senses through artificial sensors for geomagnetism, ultraviolet, radio waves, ultrasonic waves and so on,” says Yuji Ikegaya of the University of Tokyo in Japan, head of the team that installed and tested the 2.5-gram implant. “Ultrasonic and radio-wave sensors may enable the next generation of human-to-human communication,” he says.


Psychic GPS

The neuroprosthesis consists of a geomagnetic compass – a version of the microchip found in smartphones – and two electrodes that fit into the animals’ visual cortices, the areas of the brain that process visual information.

Whenever the rat positioned its head within 20 degrees either side of north, the electrodes sent pulses of electricity into its right visual cortex. When the rat aligned its head in a southerly direction, the left visual cortex was stimulated. The stimulation allowed blind rats to build up a mental map of their surroundings without any visual cues.

During training, blind rats equipped with digital compasses improved at finding food rewards in a five-pronged maze, despite being released from one of three different arms of the maze at random each time.

After two days and 60 maze trials, they could navigate their way to the reward as fast as sighted rats could. Blind rats with no additional senses, by contrast, were much slower to locate the reward and didn’t show any improvement. If they were relying on their sense of smell to find the food then all three groups would have shown similar abilities.

As further evidence that the rats weren’t simply checking each of the maze arms in turn, the team looked at what the rats did at the first turn they came across. The blind rats always went straight, no matter where they started, suggesting that they were using a fixed foraging strategy. The sighted rats and the compass-equipped rats varied their behaviour depending on where they started from, suggesting they had a map in their head that they were able to rotate depending on their location.

The rats were equally adept at navigating when electrical pulses were fed into the part of the brain that registers whisker touch, suggesting that even non-vision senses can be redeployed for navigation.

Sensory extension

Ikegaya says he has no idea how the implanted rats are “seeing” their way around. But he says that the outcome shows how adaptable the brain is. “Perhaps we don’t make full use of our brain because of the poor sensory organs it relies on,” he says. Perhaps if we could tap into its extra capacity, the real sensory world could be a lot more colourful than we currently experience, he speculates.

Other researchers agree that such sensory extensions might be feasible. “In theory, it would be possible to augment human perceptual capabilities using this approach, but many more studies in animals have to be done before one can justify any human study,” says Miguel Nicolelis of Duke University in Durham, North Carolina, who demonstrated two years ago that rats with a brain implant can learn to “touch” infra-red radiation.

People with paralysis who use a computer interface implanted in their brain to communicate or move their limbs, for example, get accustomed to using them without thinking, says Christopher James, a biomedical engineer at the University of Warwick, UK. This may be what is happening in the rats. “There’s evidence to show that such stimulation becomes ‘second-nature’,” he says.

Journal reference: Current Biology, DOI: 10.1016/j.cub.2015.02.063