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Up, down, left, right: our brains map exactly where we are in the world (Image: Mihaela Ninic/plainpicture)

We rely on brain maps to tell us where our bodies are, says Making Space, a clever book that explains the making of the maps

I GREW up using maps. My family moved often, and maps helped me reorient each time. I still turn to them to navigate the tangled streets of Boston. But my sense of direction comes from spatial orientation, not from memorising a series of right and left turns, which I鈥檓 sure to botch somewhere along the line.

Making Space purports to explain how that spatial orientation works. But Jennifer Groh鈥檚 wonderful book offers a much broader insight into how the senses we think of as separate gather information on our environment, and how nerves and the brain process the information to map our bodies and the world.

Groh starts with vision. To get in the mood, try this. Close your eyes, stretch out your arms, wave your hands, and touch the tip of a finger to the end of your nose. You can鈥檛 see your fingertip move on its twisted path, but it still reaches its destination with surprising accuracy. Our vision tells us where objects are around us, our nerves where our arms are, and our brains combine that information into the mental map that guides your finger to the tip of your nose.

Hearing is next. Outdoors we can pinpoint the crack of a broken branch or the bang of a car crash because the sound reaches each ear at slightly different times. Presumably, that was good enough to help our ancestors evade hungry lions. But why, Groh asks, can鈥檛 we pinpoint the periodic beeps of a smoke detector with a dying battery unless we are in the middle of the room as it beeps? Our sound location system, she concludes, is confused by the noise bouncing off walls, obscuring its original direction.

聯Why can鈥檛 we pinpoint the beeps of a smoke detector with a dying battery unless we are in the same room?聰

Our sensory systems have considerable redundancy. You may think your sense of direction comes from your eyes, but much of it comes from fluid-filled structures in your inner ear called the vestibular system. These are nature鈥檚 gyroscopes and accelerometers that help you keep your balance, and detect how fast and in what direction you are moving. Your muscles may sense which way you鈥檙e walking, but the vestibular system can tell your direction even if you鈥檙e in a wheelchair. Alcohol makes you wobbly because it dilutes the liquid in your inner ears, changing the vestibular system鈥檚 reaction to movement. Motion sickness is the brain鈥檚 reaction to conflicting signals when your balance system records a ship鈥檚 motion but your eyes say that you are sitting still.

But our sensory mental maps are more than just a navigation system. Part of the brain called the hippocampus tracks the body鈥檚 location, a phenomenon called a place field and discovered in rats by neurologist John O鈥橩eefe in 1971. Damage to the hippocampus prevents it from keeping track of location and forming new factual memories. That explained the case of a man called HM who could not remember events after surgery for epilepsy destroyed much of his hippocampus.

That also explains another legacy of my childhood. I don鈥檛 associate memories with a time, but with the house we lived in then. It鈥檚 a convenient way to order memory that makes good evolutionary sense, helping our ancestors remember where to find food 鈥� and avoid predators.

It鈥檚 a fascinating subject that Groh describes well, with a minimum of polysyllabic bio-speak. It鈥檚 also an important one. Shortly after I dug into the book, O鈥橩eefe shared the 2014 Nobel prize in physiology or medicine with psychologist-neuroscientist team May-Britt Moser and Edvard Moser. They discovered grid cells, another part of our internal navigation system.

Making Space highlights why they were honoured. More importantly, it explained the complex and essential interaction between the sensory system and the brain, which we are only beginning to understand.

This article appeared in print under the headline 鈥淚 am floating in space鈥︹��