Tuesday, 30 April 2024
The so-called second brain in your intestines
After I deliver lectures about the human brain, one question that people often ask me is, “Is there really a ‘second brain’ in my belly, and if so, how is that possible?” I have to tell them that for someone like me, who many years ago did his master’s research on an invertebrate—more specifically, on a marine mollusk called the sea slug—there’s nothing surprising about finding neurons in parts of the body besides the brain. Because, like my sea slug, the phylogenetically oldest animals on Earth began by having clusters of neurons (what are often called ganglia) in many different parts of their bodies. For example, the sea slug has ganglia in its mouth, feet, and brain (where the ganglia are no bigger than anywhere else) as well as in its abdomen . It was only later in evolution, and especially in vertebrates, that increasing cephalization occurred: a concentration of neurons in the rostral portion of the neural tube (in other words, in the head). But that doesn’t mean that the other neurons, such as those in the abdomen, disappeared!
We humans still have networks of neurons (known as plexuses) that are located in the walls of our intestines, that control our digestive systems, and that scientists refer to collectively as the enteric nervous system. These neurons can function independently (for example, to control peristalsis—the muscular contractions that move food down our digestive tracts), but are still subject to the influence of the vegetative nervous system.
Personally, I think that it’s a pretty big exaggeration to call the enteric nervous system a “second brain”. This system has only about 500 million neurons in all, which is about 175 times less than the 86 billion neurons in the brain, though still five times more than in the human spinal cord and and about two-thirds the number in a cat’s entire nervous system.
From the Simple to the Complex | Comments Closed
Thursday, 4 April 2024
The Brain Is Not a Space Shuttle
Recently, someone made me aware of an impressive graphic that attempts to use current neuroanatomical data to show how the brain’s circuits are interconnected, somewhat like the graphics that biochemists use to represent cellular metabolism.
I have never before seen any schematic representation of the brain’s circuits that pulls together so much information, both in its detailed version and in its simplified version, which shows the brain’s main circuits in the sagittal plane. The box in the lower left-hand corner of this graphic states that the research required to develop it was done by an aerospace engineer who had worked on the design of the space shuttle’s guidance system and who spent over four years analyzing over 1000 neuroscientific studies to prep this schematic. (more…)
From the Simple to the Complex | Comments Closed
Tuesday, 12 March 2024
How “awe” contributes to our well-being
In November 2023, many music fans in Quebec and elsewhere were saddened to hear that Karl Tremblay, lead singer of the folk-rock group Cowboys Fringants, had died of prostate cancer at age 47. Many of his fans remembered the moments of magic that they had experienced at the group’s concerts—the feelings of true oneness that only music can provide. People often have similar, fleeting experiences of wonder when out in nature—for example, beholding a beautiful sunset, or a sky full of stars or the view from the top of a mountain—or with the help of magic mushrooms or other psychedelic substances. The term “awe” is often used quite aptly to refer to these experiences when we feel part of something greater than ourselves, with a mixture of admiration and amazement, along with some fear, reverence and respect. (more…)
The Emergence of Consciousness | Comments Closed
Monday, 19 February 2024
Determined: A Science of Life without Free Will
This week I’d like to tell you about one of my “travelling companions” who has had a huge influence on me for as long as I’ve been writing popular science. His name is Robert Sapolsky, he’s a neurobiologist and primatologist, and I’ve posted about him before here and here. He has just published a new book, Determined: A Science of Life without Free Will , following his earlier, sensational book Behave, published in 2017. (more…)
From Thought to Language | Comments Closed
Monday, 29 January 2024
An interview that capture some of the essential aspects of my book to be published this fall
Today I’d like to tell you about an interview with a researcher whose thoughts run in exactly the same direction as those in the book that I’ve been writing since 2020. This book will be published this fall by
Écosociété. (I don’t know whether I’ve mentioned this book in the English version of this blog before, but it’s being published in French, and if you’re interested and can read French, I’ve been maintaining an “author’s log” about the process of writing it, in the French version of this blog). (more…)
From Thought to Language | Comments Closed
