The 21st Century Brain: How to Future-Proof Your Mind in the Age of AI, from the Sunday Times Bestselling Neuroscientist

by Hannah Critchlow

ONE OF NEW SCIENTIST'S BEST BOOKS OF THE YEAR SO FAR : 'Serious and impressive … Critchlow deserves praise for her rigour and optimism'

THE INSTANT SUNDAY TIMES BESTSELLER


Discover the powerful, practical and optimistic guide to strengthening your mind for the modern world and thriving in the age of AI, from acclaimed neuroscientist and Sunday Times bestselling author Dr Hannah Critchlow.

'An engaging, accessible and optimistic look at how neuroscience can help us navigate the challenges of this century.' - Daily Mail


'Full of fascinating new research. Profoundly empowering.' – Professor Hannah Fry, bestselling author of Hello World

How do we nurture our brains – and our children’s brains – so we have the resilience to thrive during the coming wave of technological and societal change? How can we keep up in the face of AI?

The 21st Century Brain provides the answers.

In her empowering and practical new book, bestselling neuroscientist Dr Hannah Critchlow takes you on a journey through the fascinating landscape of the latest neuroscience research, detailing how we can develop the essential human skills that technology cannot replace – and that matter most for personal fulfilment, wellbeing and long-term success.

Grounded in the latest science, you’ll discover how to strengthen and future-proof essential skills,




Emotional intelligence and collaborationImagination, creativity, and flexible thinkingLong-term thinking and decision-makingAdaptability and mental resilienceIntuition, loyalty, and connection



Writing in her informative and accessible voice, Dr Critchlow shows why our greatest strengths lie not in competing with machines, but in becoming more fully human.

Blending fascinating research with practical advice and simple brain exercises, The 21st Century Brain is the must-read guide to navigating rapid technological change with confidence.

'Fascinating neuroscience that is also a guide to modern life ... Brilliant. - Dr Darragh Ennis, neuroscientist and professional quizzer

'A vital book for understanding how our brains can adapt and thrive in an age of innovation.' – Joseph Jebelli, bestselling author of The Brain at Rest

Genres: Nonfiction, Psychology, Science

392 pages, Kindle Edition

First published April 30, 2026

Reviews

[Anna · Rating 2.75 out of 5]

Some really great insights into the brain but also quite repetitive with its advice

[Захарченко Віктор · Rating 4 out of 5]

центральна інтуїція книги витримує перевірку краще за окремі її приклади. Вона полягає не в тому, що мозок чарівний, а в тому, що він пластичний. Що невизначеність, якої ми так боїмося, – це не загроза, а саме те середовище, у якому народжуються інновації, креативність і зміни. Орган, який щосекунди фільтрує одинадцять мільярдів бітів, добудовує реальність із власних припущень і боїться незнання сильніше за біль, – це той самий орган, який винайшов письмо, побудував міста й створив машину за власною подобою. Питання двадцять першого століття не в тому, чи переможуть нас машини. А в тому, чи згадаємо ми вчасно, на що здатна та дивна, енергомістка, соціальна, схильна до блукань штука в нас на плечах – якщо перестати з нею змагатися й почати її розуміти.

[Justin Drew · Rating 5 out of 5]

Wow, what a book. In Hannah Critchlow's book ‘21st Century Brain’ her central message is that the brain is neither fixed by genetics nor entirely shaped by environment. Instead, nature and nurture interact continuously throughout life. Thanks to neuroplasticity, the brain remains adaptable and can be strengthened or weakened by our experiences, relationships, learning, diet, exercise, sleep, emotions, and environment.
- In a world increasingly shaped by AI, technological change and uncertainty, success depends less on memorised knowledge and more on developing cognitive flexibility, emotional intelligence, creativity and divergent thinking, social intelligence, resilience and lifelong learning habits

HOW THE BRAIN WORKS; The brain does not directly experience reality. Instead, it receives sensory information and constructs a working model of the world through billions of interconnected neurons.
- The brain weighs approximately 1.4kg.
- It contains about 86 billion neurons.
- These form around 86 trillion neural connections (the connectome).
- Electrical signals travel at up to 120 mph.
- Babies brains make 1million connections every second
- Human success is linked not simply to intelligence but to our capacity for cooperation, communication and collective problem-solving. Critchlow argues that humans thrive because we share knowledge and increasingly rely on collective intelligence.

NEUROPLASTICITY: "USE IT OR LOSE IT": One of the book's most important themes is that the brain remains adaptable throughout life. Neuroplasticity means learning physically reshapes neural networks, new experiences create and strengthen connections, curiosity, movement, social interaction and sleep support brain growth. Lack of stimulation leads to weakening connections and cognitive decline. The brain changes according to how it is used.

EMOTIONAL INTELLIGENCE IS ESSENTIAL: Critchlow challenges the idea that emotions interfere with rational thinking.
Instead, emotions: provide valuable information, influence decision-making, shape learning and memory and guide behaviour.
- Emotional responses arise from a combination of: genetics, environment, life experiences, and social influences.
- Humans also experience emotional contagion, unconsciously absorbing the emotions of those around them.
- Developing emotional intelligence involves self-awareness, emotional regulation, empathy, compassion and understanding others.
- Under chronic stress, creativity narrows, flexibility decreases, and negative thinking increases emotional intelligence and therefore becomes a crucial 21st-century skill.
- Emotions are information sent via signals that erupt from our body and are then analysed by our mind. They are the outputs of distinct electrical signatures in our brain, converging to guide our behaviour and influence our decision-making.

THE GUT-BRAIN CONNECTION: The brain and gut communicate through the gut microbiome, the immune system and the vagus nerve.
- A healthy microbiome appears to support emotional regulation, mood and cognitive performance
- Potential threats include ultra-processed foods (UPFs), excess sugar, poor diet and excessive antibiotic use.
- Critchlow discusses evidence suggesting disruptions to the gut microbiome may influence mental health, although conditions such as ADHD and autism remain highly complex and multifactorial.
- The gut Microbiome might play a factor and helping people to regulate their emotions and have a better emotional awareness. Feeding the gut ultra processed foods (UPF) will damage something that helps support our immune system (may be up to 70% of our gut impacts on supporting our immune system. Our gut and brain communicate via the vagus nerve. and I do think there is a probable link because of the amount of junk food we consume.
- Antibiotics strip away our gut Microbiome and when they've compared in control studies between people who've had antibiotics and those who haven't, the influence on the gut have sometimes shown that this impact has lasted for up to 7 years in reducing the cognition ability of the brain and thinking and creative problem-solving.

HUMANS ARE SOCIAL BRAINS: Human brains evolved for connection. Strong social relationships are associated with better wellbeing, improved cognition, lower dementia risk and greater resilience.
- Loneliness and social isolation are linked with poorer physical and mental health outcomes.
- Collaboration often produces better solutions than individual effort because much of human intelligence emerges through interaction with others.
- Effects of loneliness: loneliness can have a significant impact on our wellbeing. Isolation and loneliness is the equivalent of having 15 cigarettes a day. Isolation in adults shows there is an increase of 26% of those people developing dementia than over those you have strong social connections.
- One particularly interesting area discussed is the relationship between brain structure and behaviour. Research suggests that differences in certain brain regions may be associated with the ways people think, including their political attitudes and ideological beliefs. This highlights the complex interaction between biology, experience, and decision-making.

CREATIVITY AND DIVERGENT THINKING
Critchlow argues creativity will become increasingly valuable in an AI-driven world.
Divergent thinking involves generating multiple possible solutions rather than searching for a single correct answer.
Creative abilities are strengthened through imagination, brainstorming, storytelling, curiosity, and exploration.
- Importantly, creativity often flourishes during periods of mental relaxation such as walking, listening to music, daydreaming, washing dishes, resting or just looking at a blank ceiling and seeing where it takes your mind and thoughts.
- The relaxed brain frequently makes connections that focused effort misses.
- There's an interesting experiment to look for divergent thinking. Asking volunteers to come up with as many ideas that they can for the use of a rolling pin or a flowers vase and by coming up with more examples, they will show greater divergent and creative thinking. This can also be shown in which people will come up with the most ideas by using EEG to look at their brainwave activity so there is a link again between how we develop these skills within brains to how we can become more creative and divergent in our thinking in regard to looking to solutions the problems.

SLEEP, DREAMS AND CREATIVITY: Sleep plays a vital role in learning, memory consolidation, emotional regulation, and creativity
- Critchlow suggests dreams may help maintain cognitive and visual systems and contribute to problem-solving.
- Practical recommendations include keeping a notebook by the bed, recording dreams, and capturing ideas that emerge before sleep or upon waking.

ADHD, AUTISM AND NEURODIVERSITY: The book adopts a strengths-based perspective on neurodiversity. Potential strengths associated with ADHD include creativity, intuition, hyperfocus and novel idea generation.
- While challenges may include distractibility and impulsivity, Critchlow emphasises that diverse cognitive styles bring significant value to teams and society.

EDUCATION NEEDS MORE CREATIVITY AND PLAY: Critchlow argues modern education overemphasises exams, memorisation and standardised testing and underemphasises play, exploration, creativity and social learning.
- She advocates integrating arts and sciences rather than treating them as separate domains, arguing this promotes innovation and adaptability.

ATTENTION, BIAS AND UNCERTAINTY: The brain uses shortcuts and heuristics to simplify a complex world. While efficient, these processes can contribute to cognitive biases, misinterpretations, oversimplified thinking, and conspiracy beliefs.
- Advanced thinking requires tolerating ambiguity, holding multiple perspectives and accepting uncertainty

STRESS, RESILIENCE AND EARLY EXPERIENCES: Stress is not always harmful. Short-term stress can improve focus, enhance learning and boost performance.
- However, chronic stress can damage memory, reduce neuroplasticity, and impair creativity and flexibility.
- Early life adversity may influence mental health and stress responses, possibly through epigenetic mechanisms. However, Critchlow stresses that adversity does not determine destiny and that resilience can be developed.
- Early adversity: Research suggests adverse childhood experiences may influence mental health, behaviour, and / or stress responses.
- Some effects may even occur through epigenetic changes passed between generations. Importantly, adversity does not determine destiny and people differ greatly in resilience.
- Research with mice found that early-life stress, such as disrupted care from their mothers, chaotic environments, trauma, and poor nutrition, led to depression-like behaviours. Some of these effects were passed on to subsequent generations through changes in gene expression, with signs of depression continuing for up to five generations, even when later generations were raised by non-traumatised mothers. See also the Dutch famine during WW2 where parents not only passed on genetic changes to their children but this was also passed this on to their grandchildren.

NATURE AND WELLBEING: Time spent in nature appears to reduce stress, improve focus, restore attention, and enhance wellbeing. Even brief exposure to green spaces can have measurable benefits for mental performance and emotional recovery.

DIET AND BRAIN HEALTH: The brain:
- Represents only about 2% of body weight
- Uses approximately 20% of the body's energy
- Is roughly 60% fat
- Is approximately 73% water
- Diet strongly influences cognition and mental health. Beneficial nutritional principles include Omega-3 fats (especially from oily fish due to DHA), hydration, fibre, and whole foods.
- Potential risks include high sugar consumption, ultra-processed foods and refined carbohydrates.
- Poor diet is increasingly associated with cognitive decline, dementia, metabolic disease and poor mental health.
- Diabetes, in addition to all its other associated problems, is an early risk factor for later-life dementia, as numerous long-term cohort studies have shown. The UK’s Stress and Health (or Whitehall II) study was launched in 1985 and has been following the health outcomes of over 10,300 London-based civil servants ever since. Those with diabetes were found to have experienced a faster decline of 45 per cent in memory, 29 per cent in reasoning and 24 per cent in overall cognitive score than those without the condition. Similar results were found in studies from Israel and the United States.
- A remarkable piece of research shows the correlation between diet and cognition in the elderly is so strong that researchers have been able to accurately predict poorer memory and information-processing scores from an initial questionnaire about the person’s diet twelve years previously.
- Poor diet is strong linked now to poor mental health, expanding waste lines and increased cognitive decline resulting in Dementia.
- When rodents were given a high sugar diet, within five days, they were showing cognitive decline and poor memory function and inability to work out how to manage mazes. Also, when mice were given emulsifiers, commonly found in ultra processed foods, they developed changes in the gut microbiome, had thinner protective mucus in their intestines, had enhanced chronic low-grade inflammation, and were more likely to develop colon tumours in genetically susceptible mice.
- Critchlow also talks about the importance of brain function. 60% of your brain is fat and 1/3 made up of DHA which needs omega-3. It supports brain function and vision. It improves cell signalling in synapsis, so that your brain works for a much higher or able ability. This can be supported by mainly eating oily fish (or seaweed). It contains DHA which makes up a third of the fat in your brain and supports visual functioning.
- One can of fizzy pop a day increases your risk of diabetes by 28%.
- The brain is 73% water so it's also important to remain hydrated and to have drinks such as water rather than fizzy pop.
- Diet strongly affects cognition: Poor diets high in sugar, ultra-processed foods (UPF) and refined carbohydrates are linked to metabolic disease, cognitive decline, dementia risk, and poor mental health.
- Beneficial nutritional themes: Critchlow highlights: fish and omega-3 fats, hydration, fibre and whole foods.
- Brain composition: The brain is approximately: 60% fat, 73% water
- Nutrition therefore plays a significant role in maintaining healthy function.

MITOCHONDRIA: THE ENERGY BEHIND INTELLIGENCE: Mitochondria are the body's energy-producing structures. There are on average 300–400 of these organelles in virtually every cell in your body, and they play a crucial role in the way your metabolism functions; in simple terms, they act as the body’s network of power stations. Critchlow argues that intelligence may be linked partly to energy production efficiency, cellular health, and metabolic function.
- Neurons contain thousands of mitochondria because the brain is so energy intensive.
- Factors that support mitochondrial health include exercise, sleep, good nutrition and psychological wellbeing.
- Our mitochondria work hard. Across the body, they produce nearly 50kg of ATP every day. According to English biochemist Nick Lane, ‘Gram per gram, even when sitting comfortably, you are converting 10,000 times more energy than the sun, every second. The more energy your brain can produce the more intelligent you generally are.
- The reason that children are so energetic is that they are full of mitochondria but as mitochondria dies then our energy levels begin to deplete so the better and stronger your mitochondria, which is inherited down the female line, then the better the ability to create energy and intelligence.

EXERCISE AS A BRAIN ENHANCER: Physical activity is presented as one of the most powerful tools for brain health.
Exercise benefits learning, memory, mood, neuroplasticity and energy production. Critchlow highlights evidence that exercise can improve outcomes even in serious mental health conditions.

KEY PRACTICAL ACTIONS
Critchlow's recommendations include:
- Keep learning throughout life.
- Seek new experiences.
- Maintain strong social connections.
- Exercise regularly.
- Prioritise sleep.
- Eat a healthy, minimally processed diet.
- Spend time in nature.
- Practice emotional intelligence and empathy.
- Develop tolerance for uncertainty.
- Create opportunities for play and creativity.
- Journal ideas, dreams and reflections.
- Allow time for rest and daydreaming.

CONCLUSION: The overarching message of The 21st Century Brain is hopeful: human potential is highly adaptable rather than fixed. Our brains continually change in response to how we live, think, eat, move, sleep, learn and connect with others. To flourish in an age of AI, rapid change and uncertainty, we should intentionally cultivate curiosity, creativity, emotional intelligence, resilience, social relationships, lifelong learning and physical wellbeing. Ultimately, who we become is shaped by the ongoing interaction between our biology, experiences and environment.
- We are all the sum product of the energetic processes that flow through the biological structure we inhabit. We eat, and that feeds our energetic processes. We sleep and that changes our energy. We exercise and that changes our energetic state. Once we realize this about ourselves, it becomes easier to understand our relationships as another energetic process in which our respective energies influence each other.

[Reader · Rating 5 out of 5]

After a great book event session earlier in the week, I had to grab a copy of this book, and then listened to the audiobook over the weekend while doing some house chores.

The book covered so many themes important to me in my personal and professional life including: ADHD, neuroscience, nutrition, microbiome, psychedelics, creativity and critical thinking.

Dr Critchlow does a great job connecting some of the latest neuroscience with some of the challenges of our time, but doing so in an accessible way. She even provides a balanced take on how to see the positives of LLMs and how humans can play a role in working with AI as it evolves.

[Matty Evans · Rating 4 out of 5]

Enjoyed this prob up until the final chapter. Had to continuously remind myself and others that it was indeed a neuroscience book, not a self help book… was nice to read something vaguely positive re AI but I still feel quite existential tbh

[Yudeshtra Naidoo · Rating 4 out of 5]

Interesting read. Some fascinating ideas and research. I thought it lacked a bit of structure though.

[Darren Ambler · Rating 5 out of 5]

Really interesting book, down to earth advice that guides the reader through the science and highlights practical simple things you can do to help protect your brain. Well worth reading.