- The size of a human brain is unrelated to its information content, intelligence, or capacities.
- The brain never works alone.
- Cells in the body (somatic cells, immune cells) form a network that acts like a backup disk for the brain.
Ask most people what is the seat in their body for thinking, feeling, and acting, for memory or consciousness, and they’re most likely to look at you as if to say, “What a dumb question! It’s in the brain, of course.” Well, maybe not. In fact, there are instances where the brain cannot possibly account for what we know and how we function in the world.
In this post, I propose to offer extensive research that disputes the widely-held cortico-centric hypothesis of the mind and instead advances a more holistic body-mind theory, which I call the embodied mind hypothesis.
I started to explore this subject six years ago, when I read an article reprinted from Reuters Science News entitled, “Tiny brain no obstacle to French civil servant.” It seems that in July 2007, a 44-year-old French man went to a hospital complaining of a mild weakness in his left leg. When doctors learned that the man had a spinal shunt removed when he was 14, they performed numerous scans of his head. What they discovered was a huge fluid-filled chamber occupying most of the space in his skull, leaving little more than a thin sheet of actual brain tissue. It was a case of hydrocephalus, literally—water on the brain (Fig. 1). Dr. Lionel Feuillet of Hôpital de la Timone in Marseille was quoted as saying, “The images were most unusual ... the brain was virtually absent.” The patient was a married father of two children and worked as a civil servant apparently leading a normal life, despite having a cranium filled with spinal fluid and very little brain tissue.
In the animal kingdom, vast ranges in brain size fail to correlate with apparent cognitive power. Crows and ravens, for example, have brains less than 1% the size of a human brain, but still perform feats of cognition comparable to chimpanzees and gorillas. They are also able to put themselves in the position of others, recognize causalities, and draw conclusions. Pigeons can learn English spelling up to the level of 6-year-old children. Behavioral studies have shown that these birds can fashion and use tools, and recognize people on the street—things that even many primates fail to accomplish.
Some octopus species have been documented digging for and using seashells and coconut shells as tools and protection, while other species have collected rocks and positioned them in front of dens as a way to keep safe (Fig. 2). There are many anecdotal stories of octopuses escaping from tanks in aquariums and shooting jets of water at particular individuals and equipment. This may sound more entertaining than indicative of intelligence but the stories also demonstrate that the animals can recognize individual humans and show an element of planning and evaluation of their surroundings.
Octopuses lack a central brain. Each of an octopus’s eight arms has an extensive number of neurons resulting in the equivalent of having a “brain” in each appendage that is capable of receiving and processing information about the environment. These findings question a clear-cut link between brain size and cognitive skills.
The medical literature contains a surprising number of known cases of people missing a substantial portion of their cerebral cortex, the outermost layer of brain tissue, held to be the seat of our thinking brain.
In an article titled “Is Your Brain Really Necessary,” science writer Roger Lewin reviewed a series of 600 cases by pediatrician John Lorber in England of people with hydrocephalus—an excess of cerebrospinal fluid, commonly known as water on the brain. In 60 of those cases, the fluid took up 95% of their cranium (skull), and yet, half of those had above-average IQs. Among them was a student with an IQ of 126 who received a first-class honors degree in mathematics and was deemed socially normal. For this case, Lorber noted that instead of the typical 4.5 cm thickness of brain tissue between the ventricles and the cortical surface, there was just a thin layer of mantle measuring a millimeter or so. The cranium was mainly filled with cerebrospinal fluid.
Now consider the following case from China of a 24-year-old woman admitted to the PLA General Hospital in Shandong Province complaining of dizziness and nausea. She told doctors she’d had problems walking steadily for most of her life, that she hadn’t walked until she was 7, and that her speech only became intelligible at the age of 6.
A CAT scan (computerized axial tomography scans are special X-ray tests that produce cross-sectional images of the body) immediately identified the source of the problem: her entire cerebellum was missing. The space where the cerebellum should have been was empty of tissue. Instead, it was filled with cerebrospinal fluid. The patient’s doctors suggested that normal cerebellar function might have been taken over by the cortex.
In humans, radical removal of half of the brain is sometimes performed as a treatment for epilepsy in children. Commenting on a cohort of more than 50 patients who underwent this procedure, a team at Johns Hopkins in Baltimore wrote that they were “awed by the apparent retention of memory after removal of half of the brain, either half, and by the retention of the child’s personality and sense of humor."
I suggest that people with missing brain tissue who appear to act quite normally perform as well as they do not because of “neuroplasticity” or “recruitment” of unaffected areas in the brain, though no doubt some of that applies, but because the brain never works alone. Its function is inextricably linked to the body and to the outside world. In the individual who lacks a large part of their cortex, the neurons in the cranial nerves, spinal cord, and other cells in the body (somatic cells, immune cells, etc.) form a network that is constantly communicating with the brain—or what’s left of it—and acts like a backup disk on a computer, containing snippets of memory and functionality that collectively contribute to near normal cognition and behavior.
Cases of hydrocephaly provide convincing support for the argument that the size of a human brain is unrelated to its information content, intelligence, or capacities. Based on the latest advances in science, I seriously question the long-held theory of the enskulled mind and suggest instead a new holistic theory of the embodied mind.
Feuillet, L; Dufour, H; Pelletier, J ( 2007). "Brain of a white-collar worker."Lancet 370 (9583): 262.
Muenke, Max (2007). Tiny brain no obstacle to French civil servant. UKReuters HEALTH NEWS
Stacho, Martin, Herold, Christina, ... Güntürkün, Onur, et al., (2020). A cortex-like canonical circuit in the avian forebrain. Science.
Beblo, Julienne. (2018, Oct. 16). ARE YOU SMARTER THAN AN OCTOPUS? National Marine Sanctuary. Retrieved from
McClelland III, S., & Maxwell, R. E. (2007). Hemispherectomy for intractable epilepsy in adults: the first reported series. Annals of neurology, 61(4), 372-376.
Villemure, J. G., & Rasmussen, T. H. (1993). Functional hemispherectomy in children. Neuropediatrics, 24(01), 53-55;
Feng Yu, Qing-jun Jiang, Xi-yan Sun, Rong-wei Zhang; (2015). A new case of complete primary cerebellar
Lorber J. (1978). Is Your Brain Really Necessary. Arch Dis Child; Vol. 53, No 10, pp. 834-835.