The Immune Mind Quotes

“Around the time I turned thirty and was beginning to explore the science behind the gut microbiome, I decided to revolutionize my diet. In a desperate attempt to bring back the microbes I had for so long neglected, I drastically increased my fibre intake. An immediate attempt to eat thirty types of plant foods in a week just resulted in an irritable bowel and an even more irritable mood. Deducing that I’d slightly overdone things, I decided to start low and go slow. A clove of garlic here, half an onion there. Over the following weeks and months I gradually increased the diversity of plant food in my diet, slowing down if I felt that it was a bit much for my microbes to take. Within a few months I was easily eating around thirty a week, and now I no longer bother counting, as experimenting with different plant foods has become second nature. While I appreciate that I only have a study population of one, this change in diet has had dramatic effects on all aspects of my defence system. I’ve been plagued with eczema since my late teens – a disease caused in part by immune system dysfunction. Since altering my diet, it has never been better. I have also noticed positive changes in my mood and motivation, as well as a markedly improved resilience to stressors. As with all of us, life happens, and a number of difficult personal events hit me around six months after I’d established a diverse plant diet. These challenges, while difficult, did not elicit the stress responses I mounted to similar struggles a few years previously. A healthy diet is not a magic cure for life’s struggles, but it is a fantastic foundation for a resilient defence system.”
― Monty Lyman, The Immune Mind: The Hidden Dialogue Between Your Brain and Immune System

“One of the most exciting research teams exploring the relationship between gut microbes and their hosts is the Sonnenburg Lab at Stanford University, led by Justin and Erica Sonnenburg. In 2021, this power couple of the microbiome field (they’re married) and their team of scientists produced one of the most interesting studies on diet and microbes to date.9 Over a ten-week period, healthy volunteers were given a diet high in plant fibre, and a detailed analysis of both their microbiomes and immune systems was carried out. Interestingly, while there appeared to be an increase in the number of healthy microbial products (such as short-chain fatty acids), there wasn’t a significant increase in gut microbial diversity across the cohort. This doesn’t, however, contradict the evidence that fibre is beneficial for gut microbes and human health. What the stool samples of the subjects showed was evidence of incomplete fibre degradation by microbes. This confirms something that researchers in the USA had previously noticed: people who live in highly industrialized societies and eat Western diets have very low microbiome diversity. They simply don’t have the quantity or quality of bacteria to mine the gold that lies within plant fibre. Practically, this might mean that rather than dramatically increasing your dietary fibre intake overnight, you should aim for a slow but steady increase of dietary fibre over a longer time period, allowing for fibre-degrading bacteria to gradually establish a home in your gut. For many of us in the West, this is gut rehabilitation.”
― Monty Lyman, The Immune Mind: The Hidden Dialogue Between Your Brain and Immune System

“The benefits of a diet anchored in an abundance of plants is clear to see. The healthiest and longest-lived societies are scattered across the globe, whether it be the mountain villages of Sardinia, the forests of Costa Rica or the Japanese island of Okinawa, but they have one thing in common: a diversity of plants in their diet. The Hadza people of Tanzania are among the last hunter-gatherers on Earth, and they probably consume a diet closest to that which humans have adapted to eat. They forage wild berries, honey and fibre-rich tubers, and eat lean, wild meat. This consumption of between 100g and 150g of varied fibre a day results in a beautifully diverse and robust gut microbiome.4 This could not be more different from the industrialized West. Americans, on average, eat around 15g of fibre a day – half of the recommended amount and ten times less than the Hadza – resulting in poor microbial diversity.5 The so-called Standard American Diet (with the apt acronym SAD) has replaced fibre-filled plants with refined grains (plants stripped of their fibre), processed meats, sugar-sweetened drinks and deep-fried food. We all know that the modern Western diet is not good for physical and mental health, but the reason is that it’s essentially an anti-biotic diet. Without providing the food for healthy microbes, we end up overfed yet undernourished. Add to this mix an overuse of pharmaceutical antibiotics and a lack of exposure to a variety of environmental microbes due to home-cleaning products and urban living, and no wonder the industrialized world is a desert for microbes. A diet low in plant-based fibre results in a vulnerable microbiome.6 This increases the likelihood that the defence system loses balance, resulting in chronic inflammation and, eventually, a host of physical and mental health conditions.7 If it’s clear that a variety of plant fibre is the key to a microbiome-friendly diet, how do we practically implement this? The American Gut Project is a large citizen science project in which individuals across the world volunteer to send stool samples for analysis by a team at University of California San Diego School of Medicine. In 2018, they published the results of over 10,000 participants, finding that eating thirty different plants a week was associated with increased microbiome diversity.8 This was regardless of whether you were vegetarian or vegan. Most of us in the West manage only around ten plants a week. While not a necessary requirement for good health, thirty a week is a sensible, evidence-based target. It’s important to remember that plant foods aren’t restricted to fruit and vegetables; nuts, seeds, herbs, spices, grains and legumes also count. While you can add as many layers of complexity as you wish, getting a diverse, healthy microbiome is really as simple as aiming for thirty types of plant a week.”
― Monty Lyman, The Immune Mind: The Hidden Dialogue Between Your Brain and Immune System

“There is plenty of evidence to suggest a correlation between dementias such as Alzheimer’s disease and excessive, long-term inflammation in the body, known as chronic inflammation. A 2010 meta-analysis (an analysis of multiple papers, combining their findings) of 1,500 individuals found that those with Alzheimer’s disease tended to have raised levels of inflammatory cytokines in their blood.5 Curiously, further studies found that levels of systemic inflammation tend to be high in the early stages of the disease but not in advanced dementia.6 We also know that suffering from multiple infections increases the risk of developing dementia.7 There is also a dose-response relationship: the more infections (regardless of type), the higher the risk of dementia.8 An intriguing study, published by researchers at Stanford University in 2023, points the finger at one specific infectious agent: the varicella-zoster virus.9 This is the form of herpes virus we met in the last chapter, which has the dishonourable role of causing both chickenpox and shingles. The team analysed data from the National Health Service in Wales, because in late 2013 the Welsh Government enacted a health intervention that doubles up as a large natural experiment: they rolled out the shingles vaccine to people born on or after 2 September 1933. Over a seven-year follow-up comparing the vaccinated to the unvaccinated, they found that the shingles vaccine reduced the chance of developing dementia by around 20 per cent. While these are early days – and this study raises as many questions as it answers – it is looking likely that infectious agents are responsible for some proportion of dementia cases. Non-infectious inflammatory stimuli also increase the risk of developing dementia, from surgical operations to chronic autoimmune diseases.10 A remarkable link between systemic inflammation and dementia was uncovered in 2016, when researchers at the University of Southampton found that those with gum inflammation (periodontitis) had a six-fold increased risk of developing Alzheimer’s disease over a six-month period.11 In summary: it appears that inflammation in the body can drive the development of Alzheimer’s disease.”
― Monty Lyman, The Immune Mind: The Hidden Dialogue Between Your Brain and Immune System

“The results of the first clinical trial of one of the new generation of anti-inflammatory drugs were published in 2013. Eminent American academic psychiatrists Charles Raison and Andrew Miller led a study at Emory University in Atlanta, Georgia, in which patients with depression were given either a drug called infliximab or a placebo.25 Infliximab is a biologic drug that targets the pro-inflammatory cytokine TNF-α and is used in a number of autoimmune conditions. But the results were disappointing: no difference in depression-score reduction between infliximab and the placebo. But when they analysed the data further, they saw that a subgroup of patients did respond well to the medication: those who tended to have a mildly raised background level of inflammatory markers. Specifically, these were patients who had a raised baseline level of C-reactive protein (CRP) – a generic marker of inflammation in the body. A later, larger study assessed the anti-IL-6 drug sirukumab on patients who had not responded to conventional antidepressants and who had raised baseline levels of CRP.26 In this group, the drug improved only the depressive symptom of anhedonia (inability to experience pleasure), though in patients with a very high background CRP, it helped relieve depression better than the placebo.”
― Monty Lyman, The Immune Mind: The Hidden Dialogue Between Your Brain and Immune System

“At the beginning of the twenty-first century, physicians such as Iain McInnes were finding out that new biologic drugs designed for inflammatory conditions like rheumatoid arthritis could treat symptoms of depression. A number of researchers have since trawled back through the results of clinical trials that tested anti-inflammatory drugs for various chronic inflammatory conditions such as rheumatoid arthritis, lupus, psoriasis, asthma and inflammatory bowel disease. They were particularly interested in trials that also reported data for symptoms of depression as a secondary outcome. The overwhelming picture is that anti-inflammatory drugs – from older, generalized drugs such as ibuprofen and aspirin to new, targeted monoclonal antibodies – tend to improve depressive symptoms.22 One study, carried out in 2020, was able to look at very detailed patient data from eighteen clinical trials and factored in patients’ physical improvements. These trials had used a range of new anti-inflammatory drugs designed to target the inflammation behind various autoimmune diseases. Two drugs in particular demonstrated an improvement in low mood, regardless of improvement in physical symptoms. These were both antibody drugs that specifically targeted pro-inflammatory cytokines: sirukumab relieves rheumatoid arthritis by targeting IL-6, and ustekinumab treats psoriasis by blocking the cytokines for IL-12 and IL-23. Here we have data to back up Iain McInnes’s observations in his arthritis clinic: anti-inflammatory medication treating the psychological symptoms of depression, regardless of the state of physical symptoms. This doesn’t just help to strengthen an argument for inflammation causing some forms of depression; it offers hope of a treatment.”
― Monty Lyman, The Immune Mind: The Hidden Dialogue Between Your Brain and Immune System

“Sickness behaviour is a mobilization of your body’s whole defence system, both neural and immune, both brain and body. It is perhaps no coincidence that the symptoms of depression specifically associated with chronically-raised inflammatory markers – fatigue, lethargy, changes in appetite, psychomotor retardation (the slowing down of physical and mental activity), an increased sensitivity to pain and sleep disturbance – are the same symptoms experienced in sickness behaviour. But sickness behaviour is usually short-lived, and a bout of the flu does not clinical depression make. This leads us to a confounding question: how, for some people, does sickness behaviour become stuck?”
― Monty Lyman, The Immune Mind: The Hidden Dialogue Between Your Brain and Immune System

“We always need to be careful not to assume that correlation means causation – between 2000 and 2009 there was a 94 per cent correlation between cheese consumption per capita and the number of people who died by becoming tangled in their bed sheets.9 I doubt that Camembert directly causes linen entanglement.”
― Monty Lyman, The Immune Mind: The Hidden Dialogue Between Your Brain and Immune System

“As with any new drug, McInnes was on the lookout for side effects. One common one that he noted was remarkable: ‘Some of my patients reported a significant improvement in their mood, describing themselves as feeling as good as they had done for years. But when I examined their hands, their fingers were just as swollen as before; their knuckles just as deformed.’ In some patients, these new anti-inflammatory drugs seemed to lift mood and relieve depression, even if they did not deliver their intended outcome for ‘physical’ symptoms.”
― Monty Lyman, The Immune Mind: The Hidden Dialogue Between Your Brain and Immune System

“A large study of almost 40,000 Danes found that those diagnosed with schizophrenia had a 45 per cent increased likelihood of having previously been hospitalized with an autoimmune disease, compared with healthy controls.18 A similar Taiwanese study found a 72 per cent increase.19 On the flipside, another large Danish study found that those with schizophrenia have a 53 per cent increased chance of developing an autoimmune disease.20 What could explain this link, if it isn’t caused by antibodies directly meddling with the brain?”
― Monty Lyman, The Immune Mind: The Hidden Dialogue Between Your Brain and Immune System

“Throughout history it has not been an uncommon occurrence for doctors (and they were invariably all men) to remove the uterus of a woman presenting with ‘hysteria’. In some cases this must have worked, but not in the way they hypothesized. By unknowingly removing an ovarian teratoma – the tumour that sparks the formation of anti-NMDA antibodies in some cases – these surgeons had unintentionally stopped the production of the rogue antibodies that were targeting both tumour and brain.”
― Monty Lyman, The Immune Mind: The Hidden Dialogue Between Your Brain and Immune System

“Belinda Lennox had found patients whose psychiatric symptoms were caused by the immune system attacking the mind. The disease was hiding in plain sight. When Dr Najjar correctly diagnosed Susannah Cahalan in 2009, he guessed that roughly 90 per cent of those with anti-NMDA encephalitis were undiagnosed. The general consensus today is that this percentage is probably lower, but it’s still highly likely that the number of misdiagnosed cases still heavily outweighs those successfully treated. A whole decade on from Susannah Cahalan’s case, when Samantha Raggio started to believe that a Mexican drug cartel was after her family, it still took numerous reviews by medical professionals to reach the correct diagnosis. We can be certain that there are individuals with this disease today who, misdiagnosed, are missing out on life-saving treatment. As Susannah writes in her memoir, ‘How many people currently are in psychiatric wards and nursing homes, denied the relatively simple cure of steroids, plasma exchange or more intense immunotherapy?”
― Monty Lyman, The Immune Mind: The Hidden Dialogue Between Your Brain and Immune System

“Cryan’s next experiment was designed to answer the question, ‘If we believe that the secret to healthy brain ageing is through the microbiome, then we should be able to take the microbiome from young animals and give it to old animals and rejuvenate the brain.’ And it worked: by transplanting the microbiomes of younger mice into elderly rodents, his team were able to reverse age-related immune changes in the animals’ brains and improve cognition and ageing-related anxiety.47 This seems far-fetched, but since its publication in 2021 two independent teams have replicated its findings. It seems that faecal transplants rejuvenate the ageing brain.”
― Monty Lyman, The Immune Mind: The Hidden Dialogue Between Your Brain and Immune System

“One curious hypothesis, which John Cryan is exploring, is that microbes might make their hosts more social in order to maximize their ability to travel and reproduce.42 If we are huge microbial ships, what’s not to say that microbes could be at the helm? Perhaps these forces even influence kissing behaviours: it certainly can’t do much harm to sample another microbial world before the establishment of a longer-lasting connection. An intimate ten-second kiss results in the transfer of around 80 million bacteria.”
― Monty Lyman, The Immune Mind: The Hidden Dialogue Between Your Brain and Immune System

“Interestingly, there has been a large increase in the prevalence of ASD in recent decades that is not fully explained by increase in diagnosis. In 2019 a team at the California Institute of Technology suggested that one cause may lie in the gut microbiome. They were able to bring about repetitive behaviours and reduced sociability in young mice by transplanting the microbiomes of humans with ASD.39 The microbes in the intestines of these mice produced insufficient quantities of 5-aminovaleric acid (5AV) and taurine, molecules crucial for the synthesis of GABA, a neurotransmitter implicated in ASD. Other research showed that mice with ASD-like behaviours caused by induced maternal inflammation have their symptoms dramatically reduced if they are given healthy gut bacteria.40 But mice are not men, and there isn’t yet compelling evidence that gut dysbiosis causes or contributes to autism. It is, however, widely agreed that humans with ASD tend to have less diverse gut microbiomes than the rest of the population. What is debated is whether this is independent of food intake, or whether it is simply the result of more selective palates.”
― Monty Lyman, The Immune Mind: The Hidden Dialogue Between Your Brain and Immune System

“There seems to be an initial developmental phase between three and fourteen months, as breastfeeding establishes a microbiome full of healthy bacteria but one that is not hugely diverse, before a transitionary period from fifteen to thirty months, in which the microbiome diversifies and then stabilizes. Perhaps an infant’s frenzied oral exploration – from eating dirt to licking the cat – is a way of sampling their environment to diversify their gut microbiome, train their developing immune system and, ultimately, fine-tune their body’s defence system. By the time you are three years old, you have unintentionally calibrated your body’s defences. Microbes are our teachers, and they are integral to the development of a healthy immune system and a healthy mind.”
― Monty Lyman, The Immune Mind: The Hidden Dialogue Between Your Brain and Immune System

“In fact, a study that analysed over 12,000 stool samples from around 1,000 infants over the course of their early childhood found that the most significant influence on the gut microbiome is breastfeeding.32 Human breast milk contains the highest complexity of sugars of any mammal. What is truly extraordinary is that the human intestines are incapable of breaking down long sugars (called oligosaccharides) and digesting them into the molecules that are vital for body and brain health. Not so for our gut microbiome. This may at first seem utterly bizarre, but a significant portion of breast milk is not food for the baby, but for its gut bacteria. The nourishing of bacterial life is necessary for the nourishing of human life; we can’t separate the two. It is also apparent that some bacteria – potentially even from the mother’s gut – are found in breast milk.33 Breastfeeding is strongly associated with positive health outcomes, including mental health. It is associated with improved cognition in children and teenagers, and while there may be other factors at play, this finding remains even when numerous socioeconomic factors are taken into account.”
― Monty Lyman, The Immune Mind: The Hidden Dialogue Between Your Brain and Immune System

“It appears that those born by Caesarean section (C-section) are more prone to allergies later on in life,28 but it is hard to tell whether it is the method of delivery itself that causes this, or the fact that those born by C-section are more likely to have had in-utero problems or mothers with pre-existing health issues. Still, one argument in favour of the delivery hypothesis is that those born by C-section are more likely to have an unbalanced microbiome that is inadequately diverse and that can harbour opportunistic pathogens.29 This persists for at least the first year of life and the effects may last longer. This early dysbiosis (an unbalanced microbiome) may result in a poor learning experience for the young immune cells in the gut’s military academy. When stimulated, the immune systems of those who have been born by C-section produce inappropriately high inflammatory markers compared with vaginally-delivered babies.30 This is an immune system that has not developed tolerance; one that is inappropriately skewed towards inflammation. Remarkably, but perhaps not surprisingly, the mental part of the defence system also becomes hypervigilant. A 2022 study found that adults who were born via C-section were more likely to exhibit a stronger psychological stress response, as well as a greater immune response, to both short-term stressors and during a longer-term period of stress, such as exam season.”
― Monty Lyman, The Immune Mind: The Hidden Dialogue Between Your Brain and Immune System

“An important study, published in 2022 by researchers at the University of Pittsburgh, found that if you transplant the microbiomes of different types of wild rodents (herbivorous, carnivorous or omnivorous) into germ-free mice, you can determine their type of foraging behaviour and what they choose to eat.18 Germ-free mice also have an insatiable appetite for sugar, which is dampened following the introduction of a microbiome.19 These findings have been experimentally seen in other animals, and while conclusive studies on humans are lacking, it is plausible that microbes have some say in setting the menu.20 This might explain why our cravings for certain foods change following significant dietary alterations. Different microbes have different tastes – Bacteroidetes love fat, Prevotella have a penchant for carbs and Bifidobacteria are addicted to fibre – so the makeup of our gut microbiome probably both reflects and influences our food choices. An addiction to fast food might partly be down to fat- and sugar-loving microbes in your gut making persistent delivery requests. As behaviour – including willpower – is partly microbial, if you want to change your diet to improve your health, perhaps altering the microbial environment is better than simply relying on willpower.”
― Monty Lyman, The Immune Mind: The Hidden Dialogue Between Your Brain and Immune System

“Microbiome transplants might one day provide an option for mental health treatment for humans – either in the form of enemas or ‘crapsules’. One curious 2011 study found that these transplants help normalize the social lives of germ-free mice. Alongside abnormal stress and anxiety responses, it is well known that germ-free mice tend to be loners, exhibiting significantly reduced social engagement and a lack of willingness to explore their environment. This study, however, found that if you transplant the microbiome of a healthy mouse into its germ-free cousin, the germ-free mouse springs to life and begins exploring its environs.13 A few years after that study, John Cryan’s team transplanted the microbiota of humans with depression into rats, which brought about depressive behavioural symptoms in the rodents.14 This was not just a microbiome transplant: it was a cross-species depression transplant.”
― Monty Lyman, The Immune Mind: The Hidden Dialogue Between Your Brain and Immune System

“Further studies from Cryan’s lab revealed that germ-free mice had a messed-up relationship with anxiety. One study found that they had reduced anxiety-like behaviour compared with normal mice, which, on the face of it, sounds like a rather good thing. But it soon became clear that their fear-related recall – their ability to recognize threatening stimuli – was impaired.9 When regular mice were given an electric shock directly after a tone, they learned to associate the tone with the shock, to the point that when they heard only the tone they froze, anticipating the shock to come. This is a case of Pavlov’s classical conditioning. Germ-free mice, however, didn’t learn to associate the tone with pain, and continued as normal. If these mice, however, were given gut bacteria, they showed a normal, appropriate anxiety response. But, like their earlier study exploring excessive stress in germ-free mice, these effects were only seen if the gut bacteria were given early on in life, suggesting a critical developmental window. Later studies found a potential source of these odd behaviours: the amygdala, two almond-shaped clusters of nerves located deep within the brain (amygdala being the Greek for ‘almond’), each located a few inches directly behind each eye. These play key roles in emotional response to stimuli, including ‘fight or flight’. The amygdala of germ-free mice, however, is unusually large and has multiple abnormalities in its structure.10”
― Monty Lyman, The Immune Mind: The Hidden Dialogue Between Your Brain and Immune System

“In 2004, a group of Japanese scientists carried out a groundbreaking study. They compared the brains of germ-free mice to those raised with gut microbes.5 They found that germ-free mice are more stressed: they produced abnormally high levels of the stress hormone corticosterone (a rodent’s equivalent of cortisol) compared with normal mice. The scientists discovered that they could resolve this by feeding the mice the probiotic (health-conferring) bacterium Bifidobacteria infantis. Conversely, when the germ-free mice were given the pathogenic bacteria Escheria coli, they exhibited an even higher hormonal stress response. Germ-free mice also had lower levels of brain-derived neurotrophic factor (BDNF), a protein critical for learning and memory formation. Intriguingly, the scientists found that treatment with probiotic bacteria only reduced stress if given in the first few weeks of life, suggesting an important early period in which gut microbes help sculpt the brain’s stress circuitry.”
― Monty Lyman, The Immune Mind: The Hidden Dialogue Between Your Brain and Immune System

“Our ancestors would frequently be exposed to mortal peril and have to mount stress responses that resulted in memories of the threats, adaptive behaviours and immune responses. The threats facing most people in the modern world tend not to be of extreme, existential violence, but are a slow-but-steady drip-feed of stress: busy corporate life, unemployment, mortgages, insomnia, constant comparison on social media, to name just a few. These often activate an inappropriate immune response, the long-term consequence being chronic inflammation. The speed of technological development over the past century has, in evolutionary terms, transported humanity to a foreign, unnatural world. No wonder it is so easy for our defence systems to become unbalanced, miscalibrated and – in many cases – hypersensitive.”
― Monty Lyman, The Immune Mind: The Hidden Dialogue Between Your Brain and Immune System

“But this came at a cost: some of these genetic variants are risk factors for the autoimmune diseases rheumatoid arthritis, lupus and Crohn’s disease. In the same way that the military culture of a society is inherited from generation to generation – ranging from open and tolerant to hostile and defensive – the culture of our defence system is passed down to us through DNA. One positive consequence for our ancestors living in filth was that, from an early age, their immune systems were vigorously trained to differentiate friends (food and ‘good bacteria’) from pathogenic foes. In today’s sanitized, antibiotic society we are less likely to have this opportunity to help our immune system develop tolerance, refining its predictions about what is ‘self’ and what is ‘non-self’, what is safe and what is a threat. This is the core of the ‘hygiene hypothesis’, which is a widely accepted theory to explain the staggering increase in rates of allergy and autoimmunity in the modern world.”
― Monty Lyman, The Immune Mind: The Hidden Dialogue Between Your Brain and Immune System

“The modern, developed world is experiencing an ever-growing crisis of both chronic immunological diseases and mental health conditions. Perhaps this is not a coincidence, but is instead a pandemic of unbalanced defence systems. This is partially because the bodies and minds we have inherited from our ancestors were honed to survive in a very different environment. Until the health and sanitation revolutions of the twentieth century, humans in all strata of society lived in differing layers of filth, with no access to antibiotics or vaccines. This resulted in a high infectious mortality; those who survived tended to have more aggressive immune systems, prone to err on the side of inflammation. It was also a world of constant inter-human violence and regular exposure to predatory animals. Psychologically, this would have favoured a tendency towards both anxiety about others and also depression-like sickness behaviour during infection.10 Across human history, from generation to generation, there has thus been a leaning towards an ‘inflammatory bias’.”
― Monty Lyman, The Immune Mind: The Hidden Dialogue Between Your Brain and Immune System

“Almost a century later, in the 1970s, the American psychologist Robert Ader decided to do something conceptually daring and to see whether classical conditioning worked on the immune system.7 His experiment was audaciously, heretically interdisciplinary. Ader took three groups of rats. He injected the rats in Group 1 with cyclophosphamide, an immunosuppressant that also makes one feel very sick, and at the same time fed them with sugar-flavoured water. Rats in Group 2 were also injected with cyclophosphamide but drank plain water. Group 3 were injected with a placebo and had plain water. Afterwards, all of the rats were injected with red blood cells from sheep: something that should trigger a strong immune response. After a few days, the rats were given the sugar-flavoured water to drink. Those rats that had earlier been given the horrible immunosuppressant when they last drank the sugar-water became very averse to drinking it again. This finding is not hugely surprising; it’s not uncommon to develop taste aversion to a food that once carried a bacterium that gave you gastroenteritis or to an alcoholic drink you once over-imbibed to the point of bringing it all back up again. But the curious thing that Ader found was that when these rats drank the sugar-flavoured water again – this time in the absence of cyclophosphamide – they still became immunosuppressed. Some even died. It seemed that the brain and the immune system were predicting together.”
― Monty Lyman, The Immune Mind: The Hidden Dialogue Between Your Brain and Immune System

“Our perception of being ill is not a simple reaction to being infected by a pathogen, like an alarm being set off by the movement of a burglar. Our perceptions are a product of both the bottom-up (sensations brought about by a bacteria or virus) and the top-down (our brain’s predictions of the body and the world). Perceptions are also hugely influenced by context, which itself is a mélange of bottom-up and top-down influences. All human experience is found at the meeting point between our internal model of the world and external reality. This is true for any disease that involves perception. Could you have a virus causing damage in your body and battling your immune system without your awareness? Yes. Could you be experiencing long-term symptoms of illness based on your brain’s incorrect predictions that you are still infected, long after the virus has been eliminated from your body? Also yes. Your brain is constantly interpreting your body, just as it does your surroundings. Sometimes this appraisal is very accurate; sometimes it is completely misguided. Most of the time it is somewhere in between.”
― Monty Lyman, The Immune Mind: The Hidden Dialogue Between Your Brain and Immune System

“Researchers and clinicians in the fields of psychology and psychiatry are increasingly viewing mental health conditions through the lens of predictive processing. Looking at the extremes, psychiatric diseases can be seen as disorders of inference. Over-predicting and attributing excessive salience to sensory data results in hallucinations and delusions – the fantasies that our brains are constantly generating are not kept in check by the sensory evidence that should temper them. The opposite can result in dissociation – the experience of detachment from your emotions, your body or the world. According to the predictive processing framework, what we term mental illness is the formation of a maladaptive model of the world, one ceasing to be updated by prediction errors and inflexible to changing contexts. The predictive brain also explains why humans are so susceptible to ‘confirmation bias’: it’s easier to receive information that confirms our model of the world. Let’s say, for example, that you have depression fuelled by a core belief that you are an abject failure in all areas of life. Over time, your brain turns up the gain for evidence confirming this negative belief, and does not pay adequate attention to contrary evidence suggesting that you actually do have strengths and are valued by others. These beliefs also result in behaviours, such as social avoidance, that further strengthen a belief that you have no friends and nothing to offer the world. This becomes a self-fulfilling prophecy: down and down a vicious spiral you fall. Context is also crucial. A mental health condition may result from what was once a successful, adaptive response that has been transplanted into an unsuitable environment. I once assessed an army veteran with post-traumatic stress disorder (PTSD) who, a decade after returning from a busy tour in Iraq, instinctively jumped off a road bridge in response to the sound of a backfiring car. Thankfully, the waters of a canal below broke his fall. That was a well-adapted response for war-torn Basra, but one unsuited to an uneventful, middle-class suburb of Birmingham. Following a traumatic event – whether it be war, childhood abuse, severe pain, a nasty infection – our brain’s predictive baseline can be dislocated and end up becoming hypersensitive, expecting to be in constant danger even long after the peril has passed. Essentially, if someone’s model of the world does not successfully adapt to their environment and minimize uncertainty, the result is misery.”
― Monty Lyman, The Immune Mind: The Hidden Dialogue Between Your Brain and Immune System

“The brain is not primarily there to think; it is to serve a complex and fragile body in an ever-changing world. ‘I am, therefore I think’, may be a more apt way of viewing how the brain works. This playful inversion of Descartes is a dictum used by many of those in the predictive processing field, including the British neuroscientist Karl Friston, perhaps the theory’s foremost proponent.”
― Monty Lyman, The Immune Mind: The Hidden Dialogue Between Your Brain and Immune System

“Descartes’ conception of the mind and body as utterly separate entities has seeped deep into the subconscious of Western medicine and society. Many people live as though all of one’s essence – thoughts, feelings and personality – is located in a disembodied mind, with the body relegated to the role of a fleshy robot that has evolved to look after the thinking brain. But, as we will see, this could not be further from the truth. The evidence we will encounter in this chapter has profound implications not only for the way we understand how the human organism works, but also how we view illness.”
― Monty Lyman, The Immune Mind: The Hidden Dialogue Between Your Brain and Immune System