Some myths about the brain, such as the idea we only use 10% of our grey matter, are notorious, especially among neuroscientists. These myths crop up every now and then (look at the premise of the Lucy movie this summer), but they are quickly shot down by those in the know.
In contrast to these enduring stories, other misconceptions are stealthier and slip beneath the radar unrecognised. One of these is the idea that the human brain is served by five senses. This belief is so ingrained that even the scientifically literate will treat it as taken-for-granted common knowledge.
Perhaps it is due to the idea’s noble origins. The principle of five basic human senses is often traced back to Aristotle’s De Anima (On the Soul), in which he devotes a separate chapter to vision, hearing, touch, smell and taste. Today, the five senses are considered such an elementary truth that it is sometimes used as a point of consensus before writers embark on more mysterious or contentious topics. “What do we actually mean by reality?” asked the author of a recent article in New Scientist magazine. “A straightforward answer is that it means everything that appears to our five senses.”
If only it were that simple. Simply defining what we mean by a “sense” leads you down a slippery slope into philosophy. One, somewhat vague, definition might argue that a human sense is simply a unique way for the brain to receive information about the world and the body. If that is the case, then we can claim with confidence that there are certainly more than five human senses.
First consider the senses that relate to the position of our bodies. Close your eyes, and then touch your right forefinger to your left elbow tip. Easy? How did you do it? Somehow you knew where the end of your finger was and you also knew the position of your left elbow. This sense is known as proprioception and it’s the awareness we have of where each of our body parts is located in space. Proprioception is possible thanks to receptors in our muscles known as spindles, which tell the brain about the current length and stretch of the muscles.