How much of our brain do we really use?

The human brain is as complex as it is fascinating. While neuroscience can sometimes be challenging to explain in layman’s terms, there is at least one phrase that seems to be common knowledge globally: people only use 10% of their brains. This has led to the idea that humans are sitting on limitless unlocked potential. Examples can be seen in pop culture where the dormant 90% is awakened to increase intelligence or gain superpowers, and real-life scientific geniuses have been described as using a higher percentage of their brain than the average Joe.

The aim of this article is to explore how the concept of using 10% of our brain became so widely known and whether evidence from modern neuroscience supports it.

Though the exact origin is difficult to pinpoint, Harvard psychologist William James stated as early as the 1900s that only a fraction of a person’s full mental potential is ever met [1]. Soon thereafter, the 10% value could be seen popularised in advertisements from the 1920s and in popular culture in the 1930s, from science fiction to self-help books [2] [3]. Another origin story claims it was a misinterpretation of neurological research in the 19th and 20th centuries, as theories surrounding the function and even the importance of various brain regions were still in their early stages [4]. Albert Einstein has also been credited with explaining his own brilliance by referencing the 10% idea. However, there is no official record of him stating this in the Albert Einstein Archives [5].

Regardless of its origin, the phrase in question has been around for many decades [6]. What, then, have recent neurobiology studies found out about our daily brain use?

Neuroscientists are able to assess which parts of the brain are active at a given point through special imaging techniques, such as positron emission tomography (PET) and functional magnetic resonance imaging (fMRI). The former uses a radioactive compound that marks metabolically active tissue [7], while the latter follows the path of oxygenated blood through the regions of the brain [8]. Increases in metabolism and oxygen are therefore indicators of neuronal activity [7] [8] and show what our brains are doing under different conditions. Whether we’re learning to solve puzzles [9], “resting” (i.e. doing nothing) [10] or sleeping [11], research indicates that all three major parts of the brain are active to a certain extent over the course of a day. The cerebrum has many functions, including speech, learning and sensory processing, the brainstem is involved in involuntary actions like heart rhythm and breathing, and the cerebellum controls muscle movements and balance [12].

Additionally, the different regions of the brain need to communicate in order to process multisensory information, such as sight and sound simultaneously, which can involve large areas of the brain [13]. When playing musical instruments, for example, the primary auditory cortex listens to the music [14], the cerebellum is involved in memorising sequences of movements [15] and various areas of the cortex and sub-cortex are involved in timing [16].

Furthermore, the brain is continuously working to remodel itself. As babies, we make many more connections between neurons than are necessary for a functioning adult brain, and these need to be cut back in a process called synaptic pruning. Synaptic pruning happens rapidly until puberty and more slowly through adulthood [17]. If 90% of the brain were continuously inactive and therefore unnecessary, neuroscientist Dr. Barry Beyerstein argued that the adult brain should then reveal extensive levels of degradation due to synaptic pruning, which has not been shown to be the case [18]. Similarly, the neural connections formed across different brain areas are continuously being “rewired” based on our experiences [19], so, ultimately, the brain is a very active organ.

In summary, there is an ever-increasing body of evidence contrasting the decades-old saying that humans only use 10% of their brain. Efforts have been made by neuroscientists [16] and psychologists [6] alike to dispel this notion as a myth for many years. Hence, when we ask a search engine nowadays how much of our brain we use, the first results inform us that the 10% saying is a common “neuromyth”. Advice for improving brain function is instead related to preventing mental decline as we age, such as physical exercise and performing mentally stimulating activities (e.g. crossword puzzles and maths problems) [20], rather than unlocking hitherto untapped potential.

Overall, the consensus among neuroscientists is that humans use many parts of the brain at any given time, with signals being coordinated in multiple areas of the brain through our conscious and subconscious actions.

All images are the work of Dr. Marco Garbelli, a member of the Facts&Reasons graphics team.

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