Before understanding how your brain responds to psilocybin, a basic overview of brain functions might be useful
Brain science is an evolving science. For some people talking about “the brain” seems materialistic, as if all we are is a lump of electrically charged flesh; similarly, many are uncomfortable talking about something as intangible as the mind. However, it is now widely accepted that the brain is an organ designed to change in response to experience and training. However, it is good to have a basic understanding of brain function, so let’s pop the hoodie and do a quick overview of what’s where and what it’s responsible for. So the next time someone tells you: “Psilocybin is a hallucinogen that works by activating serotonin receptors, most often in the prefrontal cortex,” you’ll know exactly what they mean.
The Brain: A Basic Owner’s Manual
Often when we think of the various parts of the brain we think of our biology textbooks from high school and the brain function chart that always looked as if it belonged more in the butcher shop than a science text. Even divided into its many parts, the brain still looked powerful. The reality is that if you ever got to poke it, it would feel like a mound of soft tofu.
At first glance, the brain is less than impressive. It’s a wrinkled grey mass whose surface resembles that of a walnut (that’s because the brain folds itself up—just as your intestines do—to fit more matter into a small space).
Appearances are deceptive, though, your brain is astoundingly complex and perpetually active. Even while you sleep, it isn’t entirely at rest, carrying on its vital role of maintaining breathing, heartbeat and other bodily functions, and dealing with bursts of increased activity as you dream. When you’re awake, the brain has truly amazing multi-tasking abilities. In an instant, it controls all your physical functions, with all your senses sensing on full alert, all while you drive your car at 90 km per hour down a busy highway, watching the road signs, remembering your route, digesting your lunch and listening to music. Not bad for a wobbly mass of grey matter.
How does it get it all done? You’d never know by looking at it, but the brain contains distinct regions, each with its own job to do. Much of what is known about how different parts of the brain work came from observing how people act and react after damage to certain areas due to injury, tumours, seizures or stroke.
Now functional magnetic resonance imaging (fMRI) measures brain activity by detecting changes associated with blood flow. It is a class of imaging methods developed in order to demonstrate regional, time-varying changes in brain metabolism. These metabolic changes can be consequent to task-induced cognitive state changes or the result of unregulated processes in the resting brain.
The entire wrinkled outer layer of the brain is the cerebral cortex, also known as grey matter. Only a few millimetres thick, it contains 77 percent of the total volume of brain tissue, much of it hidden in its many folds and convolutions. The cerebral cortex is largely responsible for all forms of conscious experience, including perception, emotion, thought and planning.
The two sides of the brain—the left and right hemispheres—further divvy up these functions. Usually in right-handed people—and generally vice-versa in left-handers—the left hemisphere controls language, while the right-side controls spatial orientation skills. It used to be thought that while writing a letter involves your left brain; painting a picture would be down to your right brain but the idea that the right brain innovates and the left brain calculates has been abandoned by neuroscientists. They now know that the right and left hemispheres are equally involved in both tasks. And there are no special creativity hot spots in the brain—the same areas that are active in everyday thinking, planning and understanding also pitch in to come up with original insights too.
Because the body’s nerves cross sides, the left hemisphere controls the right side of your body, and the right hemisphere controls the left. The two halves of your brain are connected by millions of nerve fibres called the corpus callosum. This “bridge” allows the brain to merge and coordinate skills so it can act as a united whole. If the corpus callosum is damaged or severed, the two sides of the brain can’t communicate.
Your Brain’s Communication Network
Grey matter is not a single material but a biological construct of capillaries (which carry oxygen and nutrients throughout the brain), nerve cells (also knowns as neurons) and glia, the cells that support, feed and communicate with nerve cells. Its nucleus contains genetic material (DNA) and generates proteins to maintain the neurons.
If you suck away the glia, you are left with a communications network wired from billions of nerve cells. This lacy structure underlies everything in your physical, mental and emotional life.
Life depends on neurons passing messages to other neurons. The messages from one neuron are transmitted along a single fibre called an axon and received by a multitude of short branches called dendrites. As the information passes from one neuron to the next, it must jump across countless tiny gaps called synapses. This is where brain chemicals called neurotransmitters, such as serotonin and dopamine, come into play. When information reaches the end of one neuron’s axon, they carry it across the gap to receptors on the next neuron.
As with any communication network—think about your internet service provider, or cell phone company and the satellites it uses to send information from one place to another—the better the network, the clearer the messages and the faster they are able to get through.
To transport information from one part of the brain to a more distant area, the brain uses special high-speed cables—bundles of axons coated by a fatty substance called myelin, which stands out from the rest of the brain and gives the brain’s white matter its name. The coating insulates the bundles and speeds the transmission of electrical signals along this communication expressway, allowing for faster cognitive processing.
Your Grey Matter at Work
We call brainy people cerebral for a good reason: the cerebral cortex, also known as grey matter, is where complex thought, attention and memory take place. Different functions occur in different areas.
THE DEFAULT MODE NETWORK
The “default mode network” (also the default network or DMN) typically refers to an interconnected group of structures in the brain that are thought to be part of a functional system. Because the DMN is a relatively new concept, there isn’t yet a consensus on which regions of the brain should be included in a definition of it. However, most definitions include the prefrontal cortex, the parietal lobe and/or other brain areas and neuron groups.
The DMN concept was developed several decades ago, after neuroscientists observed high levels of brain activity in experimental subjects who were supposed to be resting quietly—not engaged in any specific mental task. As fMRIs became more accurate, scientific data accumulated that suggested high-levels of brain activity during resting states.
The DMN grey matter areas manifested lower levels of brain activity when people were engaged in specific task work—such as paying attention to a school lesson or following something with your eye—but higher levels of activity when awake but not involved in any distinct mental exercise. So when a person is not focused on the outside world but wakefully resting within themselves—things which we might refer to as daydreaming or just letting our minds wander. However, the DMN can also be considered active when a person is being self-conscious, or thinking about others, remembering the past or planning for their future.
The DMN is a fascinating new area of research for neuroscientists, psychologists and more and is a key area of study for those researching the effects of psychedelics and psilocybin. We’ll be publishing lots of blogs in future about the DMN.
The part of the frontal lobe closest to your forehead is the prefrontal cortex, the primary area for keeping short-term memories (also called working memory). Think of it as a temporary filing system that holds facts for just a few seconds—a phone number you are about to text, for example. Thoughts or ideas reside here briefly unless you make the effort to commit them to long-term memory.
Decision making, planning and problem solving
The large portion of the brain called the frontal lobe is the brain’s command centre. It controls decision making, planning, organizing and problem solving. It also creates our personalities, sharpens our attention and keeps us focused on goals. It allows civilized societies to exist by putting the brakes on some of our basic instincts. Damages to the frontal lobe can result in wildly fluctuating emotions and difficulty performing even simple tasks.
At the rear of the prefrontal cortex is the primary motor cortex, controlling all movement. Brain scientist can now identify the locations in the motor cortex associated with distinct patterns of movement, such as the hand motions of musicians. In fact. It’s even possible to know what instrument a musician plays by looking at changes in this part of the brain.
The parietal lobe, towards the back of the brain, is responsible for the body’s physical sensations. A disproportionate amount of the parietal lobe is dedicated to some of the smallest—but most sensitive—parts of the body, such as the tongue, hands, face and genitals. The parietal lobe also plays a role in spatial recognition, language and our ability to focus attention. Damages to the parietal lobe can distort the way a person perceives space and objects. If the damage is on the right side, the person may be totally unaware of anything on the left of his or her visual filed, including the left side of a computer screen or even his or her own left leg.
The occipital lobe at the back of the brain manages vision. It controls eye focusing, interprets the meaning of all the shapes and colour we see and records short-term visual memory.
The temporal lobe, beneath the temples, connects to the ears and processes and interprets sounds. It also has a role in memory, particularly for words, ideas and names. Damages to the temporal lobe may render a person unable to learn new facts or remember events. Life seems eternally new (and frustrating) because no new memories can be formed. A person with this type of damage could read the same newspaper over and over again without getting bored.
Coordination and balance
The cerebellum (the ‘little brain’) is a small wrinkled area at the base of the brain. Don’t let its small size fool you—it contains half of the brain’s neurons. While the motor cortex is the area that sends messages to the muscles, causing them to move, the cerebellum acts like a conductor, coordinating all the movements that let you successfully swim a length in the pool, knit a sweater or walk down the street. Injuries to the cerebellum can cause dizziness, slurred speech, nausea and uncoordinated movements. Affected people are often mistaken for being drunk, hence the term: “drunk while sober.”
The Limbic System: Basic Instincts
Buried deep under the cerebral cortex is the limbic system, a set of primitive structures responsible for some of our most basic human instincts and drives. Craving a piece of chocolate cake? Blame, in part, the limbic system, which regulates our response to pleasure. Running away to escape a fierce dog? Thank the limbic system, which is largely responsible for our survival instincts. Terrified of bees after being stung badly as a child? The limbic system is the culprit, because it won’t let you ever forget that event. Emotional memories are often subconscious but they may suddenly pop up in the for of panic attacks or flashbacks.
The limbic system is also in charge of our most primal urges, including those of a sexual nature. Damage to this part of the brain leaves appetite, aggression and sex drive unregulated.
The limbic system may be involved in the unique phenomenon we know as “déjà vu” (literally “already seen”). This sense of having been in an unfamiliar place or of having had a conversation and lived through the moment before has been regarded by some people as evidence of reincarnation. Others have explained it as the memory of a dream in which the person “experienced” the moment in advance of it happening. Conversely, the sense of “jamais vu” (“never seen”) occurs when what is known and familiar becomes for a while strange and unusual.
Scientists now believe that both are caused by a momentary failure of the limbic system to react appropriately. When déjà vu takes place, information flowing through the limbic system is mistakenly tagged with familiarity. When this incorrectly identified information merges with information from elsewhere in the brain, it produces a puzzling sense of familiarity. Conversely, in the case of jamais vu, the information’s true emotional significance is not recognized as it should be.
This tiny area of the brain, whose shape first reminded scientists of a seahorse (hippocampus is Greek for seahorse), converts short-term memories into long-term ones. It shares responsibility with the hypothalamus for aggressive behaviour, sex drive and appetite. And it’s largely responsible for spatial memory and navigation. It’s one of the first regions to become damaged in cases of Alzheimer’s disease, causing memory problems and disorientation.
This part of the brain helps to regulate fear, anger and sexual response and is considered the integrative center for emotions, emotional behaviour and motivation—the amygdala is where you experience a “gut reaction,” those subjective feelings, about what is good and what is bad. It is also where memory and emotions are combined. The amygdala is involved in the perceptions of pleasureful emotional learning as well as fearful emotional learning. If a memory or association of something was particularly happy, or conversely a horrible humiliation, these learnings may last a lifetime.
Does your heart beat faster even when you just think about a scary upcoming event? Perhaps it’s your driving test, an exam or an important presentation to clients. That’s the hypothalamus at work. About the size of an almond, this region has an amazing amount of control over what happens in our bodies, and even over our moods and actions. It not only controls sexual arousal and behaviour but also regulates hunger and thirst, sleep and wakefulness, responses to pain and pleasure, levels of anger and aggression, and even our body temperature, pulse, blood pressure and other physical responses to emotional events.
“Human Brain,” Wikipedia.
“Default Mode Network,” Wikipedia.
“What is the Default Mode Network? A default level of brain activity sheds light on the source of consciousness and mechanisms of ego death”, Psychedelic Science Review, November 2020.
“Overview of Functional Magnetic Resonance Imaging” by Gary H. Glover, PMC, US National Library of Medicine, National Institutes of Health, 2012.
“Competitive and Cooperative Dynamics of Large-Scale Brain Functional Networks Supporting Recollection,” by Alex Fornito, Ben Harrison, Andrew Zalesky and Jon Simons, PMC, US National Library of Medicine, National Institutes of Health, 2012.