How do we navigate? Photograph: Calsidyrose/flickr
Homing pigeons are of course famous for their extraordinary navigation abilities. They can find their way home from new locations up to 1100 miles (1800 km) from their nests. There are several theories that attempt to explain the navigational and migratory skills of birds, and homing pigeons are a useful model to help us understand these extraordinary abilities.
The olfactory navigation hypothesis suggests that homing pigeons use an olfactory map to orient themselves. This is based on a study led by Silvano Benvenuti in 1972, which showed that pigeons who had their olfactory nerves sectioned could not find their way home when released from unfamiliar locations.
The magnetic map theory poses that birds get their sense of direction from the Earth’s magnetic field. The Earth’s magnetic field becomes stronger the further you get from the equator, and homing pigeons may be sensitive to these minute changes in the magnetic field strength.
The use of the sun as a compass, a bird’s circadian rhythm and the possession of an internal map are other theories that try to explain bird navigation. However, at the moment there is no clear evidence that supports any of these theories over the others, and how these internal cues might work together is also poorly understood. Sadly, the mapping skills of birds remain largely unexplained.
How do we find our way home?
Although we still don’t know the complete story, there are some very strong clues to how birds navigate. But how mammals (including humans) navigate is relatively unexplored. Recent research is however giving some very interesting insights.
The hippocampus is a sea horse-shaped structure located in the centre of the brain. It is well known for its role in memory formation, but also is important to our sense of direction and navigation. In 1971, John O’Keefe discovered the first element of a mammalian “inner-GPS” when he observed a subtype of neurons in the hippocampus that became active whenever a rat moved to a particular area of a room. These neurons, now known as “place cells” are thought to help rats – and us – build a picture of where we are in our environment.
In 1984, James Ranck made another step in explaining spatial representation in our brains. He found that mammals have “head-direction cells”: cells that fire in response to the specific angle and direction of your head’s orientation in space.
Has our sense of direction been found?
These findings have been important for starting to uncover the neural basis of human navigation (O’Keefe won a Nobel Prize for his research), and a study published just after Christmas has continued to help unravel the mystery of how we navigate.
Martin Chadwick and his colleagues at UCL asked participants to navigate around a simple virtual environment on a computer and gave them target destinations to move towards.
Using functional magnetic resonance imaging, the researchers were able to pinpoint a population of neurons that signalled the direction in which participants needed to go to their target destinations – and, the varying strengths of brain signals from these cells were able to predict subjects’ navigational ability.
Does this explain why some people have a better sense of direction than others?
These specialised neurons were found in the enterohinal cortex, a region next to the hippocampus. But although the study shows that the enterohinal cortex has greater activity in those better at navigating, the results do not really explain whythis may be.
In other words:
Are you a better navigator because you have higher activity in your enterohinal cortex?
Is the activity in your enterohinal cortex higher because you are a better navigator?
What is really driving this relationship? When we misinterpret correlation, we can find ourselves, just for example, assuming that chocolate consumption might improve cognitive function in entire populations.
Use it or lose it: why iPhones may be disrupting your navigation skills
When people use GPS-like instructions to reach a destination rather than navigating on their own, their brains in general are found to be much less active. Perhaps the less you use your phone’s GPS to help you navigate, and the more often you learn to make it on your own, the stronger the activity in your hippocampal region – and so the better a navigator you become. In Chadwick’s study, the stronger neural activity amongst the better navigators may have been a result of them having better developed their navigation skills throughout their lives.
Chadwick explains that future research will be needed to support the case for a causal relationship between neural activity and our mapping skills. He would like to see similar studies carried out in real life environments to demonstrate that these neurons extend their functions beyond those described in the virtual environment simulated for his study.
If you feel lost after reading this post, perhaps eat some chocolate – it might improve your brain power. Or, if you will, take a stroll somewhere new and try to find your way back home – without your GPS app!
Chadwick MJ et al. A Goal Direction Signal in the Human Entorhinal/Subicular Region. Curr Biol 2015;25:87–92.
This article was originally published on the Guardian Online.