Do we only use 10 per cent of our brain? Here’s what science says

Science-fiction films, ‘mind-enhancement’ courses and anecdotes about supposed hidden abilities have popularised the idea that the human brain functions at only 10 per cent of its potential, leaving a vast reserve of grey matter untapped. It is a striking and alluring notion to think we possess untapped potential which, if unlocked, could grant us extraordinary abilities. Neuroscience, however, tells a different story: even when at rest, the brain is an organ that is almost always active in its entirety…

No. This is a widely held belief that has been around for decades but has no scientific basis. A neurologist at the Johns Hopkins School of Medicine has described this belief as so wrong as to be almost ridiculous, explaining that we use virtually every part of the brain and that most of it is active almost all the time. A neurologist at the Mayo Clinic has also confirmed that, over a 24-hour period, we use 100 per cent of our brain: even whilst sleeping, areas such as the frontal cortex – involved in decision-making – or the regions that process stimuli from the body remain active. An everyday action such as pouring coffee into a cup, for example, requires the simultaneous coordination of several areas of the brain: the visual and motor areas, the cerebellum and the basal ganglia.

One of the strongest arguments against the myth is energy consumption: in the average adult, the brain accounts for around 2 per cent of body weight, yet it alone consumes around 20 per cent of the energy (in the form of oxygen and calories) of the entire body, with a metabolic rate that remains surprisingly constant regardless of how mentally or physically active one is. From an evolutionary perspective, such an energy-intensive organ – 90 per cent of which is unused – would have made no sense: natural selection would have favoured smaller, more efficient brains.

It is a common misconception, but it stems from a misunderstanding of how these techniques work. The images produced by functional magnetic resonance imaging do not show the brain’s ‘absolute activity’, but rather differential images: only those areas whose activity exceeds a baseline level during a specific task, compared with a control condition, are coloured. Take, for example, studies that aim to investigate the brain’s response to images of human faces: researchers will therefore look for those areas that become activated in a manner that is distinctive and unique to that task. The images will thus show those specific areas coloured in yellow and red. The areas that remain grey, however, are not inactive; they are in a sort of standby mode, with background activity that nevertheless continues to play a functional role. In other words, the colour-coded map shows where the brain is working ‘harder’ on a specific task, not simply where the brain is working at all.

This belief too – often used to reinforce the myth – does not stand up to scrutiny in the light of the most recent data. The idea that glial (support) cells are ten times more numerous than neurons stems from claims made in the 1960s, which were never supported by solid experimental evidence, yet were repeated for decades, even in highly authoritative neuroscience textbooks. It was not until 2009 that a more accurate cell-counting technique demonstrated that the ratio of glial cells to neurons in the entire brain is close to 1:1, with a more precise estimate of 0.7:1 – thus actually slightly lower, not higher, than claimed by the myth. Furthermore, glial cells are by no means ‘inert’: they play an active role in nourishing and supporting neurons and are also involved in the processes that underpin memory.