Brain: myths and false beliefs
I have heard many times, whether around me or on students lips : « We only use 10% of our brain capacity. » Well, no! To understand better why one of these myths about the brain is false, it is important to take some data. Our brain is made up of different parts illustrated in the diagram below.
It grows up until adulthood. At birth, it weighs the equivalent of 23% of its final weight, an average of 1.4 kg (3,08 pounds)5 once its growth is complete. Its energy consumption is substantial: 20% of that consumed by the body. And it contains 85 billion neurons, and other types of cells that we will see again. This consists of a lot of water, but also of fat. While being protected from « outside » by these barriers of water and fat as well as bone, it also has a « blood-brain » barrier that protects it from toxic attacks coming directly from the body. Another misconception, our neurons do not die before us (except in case of diseases). The neurons of a centenary are therefore a century old. In addition, these are renewed throughout our lives. This production of new neurons is called neurogenesis. It takes place mainly in the hippocampus.
Place of neurogenesis. This neurogenesis can increase with learning, as it can greatly decrease in the case of stress (see the article « When stress overwhelms us ») or with age. Electrical nervous messages are transmitted via neurons, passing through their part called axons, to emerge at their ends, the nerve endings, which allow them to connect with each other and transform this electrical message into a chemical message (neurotransmitter).
Certain neurons can exceed 1 meter in length, in particular those starting from the spinal cord and arriving at the end of the foot. Each neuron makes several thousand connections with its neighbors. There are also several thousand types of neurons: not all of them have yet been clearly identified.
However, our brain is not made up of just one type of cell. There are also glial or glia cells. We have over 100 billion. Their proportion varies according to the areas of our brain. This glia is also what is more commonly called the white substance (55% of the volume of our brain), in contradiction with the gray matter or gray substance which indicates the very body of the neuron and its termination.
This proportion in the brain of populations of neurons and glial cells varies according to the species. Depending on the phylogenetic evolution (i.e. the evolution according to the kinship between species), the percentage of glial cells / neurons increases. For example, the earthworm, has six times more neurons than glial cells than a fly, rats and humans where there is a glia / neuron ratio of 20, 60 and 120 times higher. Be careful, this does not mean that Man has higher intellectual faculties!
Among the glial cells, two types of cells are well known and studied: astrocytes and oligodendrocytes.
Oligodendrocytes are cells that produce the myelin sheaths that themselves surround the axons of neurons. This myelin sheath helps « speed up » the transmission of the neural message in electrical form.
Astrocytes perform different functions. They provide the energy supply to the neurons and participate in the communication between nerve cells. They control the formation of connections between neurons and have a role in our behavior.
Another important actor that is not a cell, the blood capillaries present in our brain. They provide food, oxygen and allow the evacuation of waste. They also have a barrier role that protects against infections and germs.
There is therefore a close collaboration between the neurons ensuring the transmission of the nervous message, the blood vessels providing the supplies and playing the garbage collectors and the astrocytes which coordinate their relationships.
So where does the best-known myth about our brain is coming from, that we use only 10% of its capacity? It was initiated by psychologist William James who stated in The Energies of Men that « we use only a small part of our possible mental and physical resources ». It is true that when our brain is in action all the regions do not fire simultaneously. However, by imaging techniques, we have been shown to use it 100% well. However, this 90% and 10% are not however invented. It’s actually the proportions of our cell types present. We thus have 10% of neurons and 90% of glial cells used to support neurons.
Neurobiology is a rapidly expanding discipline, particularly with the study of brain development in small animals to alleviate, for example, diseases such as Alzheimer’s.
It is therefore important, as in all disciplines, to be properly informed and especially to cross-reference sources in order to avoid believing and spreading scientific myths!
1.Agid, Y. & Fan, X. L’autre moitié du cerveau : les cellules gliales. Med Sci (Paris) 35, 199–200 (2019).
2.Epelbaum, J. Voyage extraordinaire au centre du cerveau : Jean-Didier Vincent. Extraordinary journey in the center of the brain (2008) doi:10.1051/medsci/2008242213.
3.Gilgenkrantz, H. Notre cerveau - Un voyage scientifique et artistique des cellules aux émotions (Hervé Chneiweiss). Med Sci (Paris) 36, 169–169 (2020).
4.Lemasson, M. & Lledo, P.-M. Le cerveau adulte : un perpétuel chantier ! M/S. Médecine sciences [ISSN papier : 0767-0974 ; ISSN numérique : 1958-5381], 2003, Vol. 19, N° 6-7; p. 664-666 (2003) doi:10.1051/medsci/20031967664.
5.Mandressi, R. Le cerveau et ses représentations dans la première modernité (XVIe-XVIIe siècles) - Représentation en sciences du vivant (4). Med Sci (Paris) 27, 89–93 (2011).
6.Ask the doctor: 10% brain myth - Harvard Health. https://www.health.harvard.edu/mind-and-mood/10-brain-myth.
7.L’homme glial : une révolution dans les sciences du cerveau. France Culture https://www.franceculture.fr/oeuvre/lhomme-glial-une-revolution-dans-les-sciences-du-cerveau.
8.Le grand Atlas du cerveau | Éditions Glénat. https://www.glenat.com/reference/le-grand-atlas-du-cerveau-9782344031537.
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