Guide
Your heart starts racing before you even know why. You jump, and then you see it was only the cat. This reaction isn’t a fault: it is a very old survival system, working together with your cortex. Here is what research says today.
The “limbic brain”: a useful but simplified image
You often hear that we have an “emotional brain” (the limbic system) and a “rational brain” (the cortex): the first inherited from animals, the second uniquely human. The idea comes from the physician Paul MacLean, who in the 1950s popularised the term “limbic system” and later the theory of the “triune brain”: a reptilian brain, a mammalian (limbic) brain and a neocortex, stacked on top of each other over the course of evolution.
The image helps us understand something true: some of our reactions are fast, automatic and come before thought. But current neuroscience corrects it on several points:
- The brain wasn’t built in layers added one on top of another: fish, reptiles and birds also have structures equivalent to our cortex. We don’t carry a “little reptile” hidden inside us.
- There is no single “emotion centre”. The amygdala, hypothalamus, insula, hippocampus and prefrontal cortex work in highly connected networks, where emotion and thought mix all the time.
- The amygdala isn’t “the fear centre”: it detects what is important (threatening, but also new or pleasant) and sets the body in motion.
A little theory · Researchers in neuroscience and evolutionary biology summed up these corrections in an article with a very telling title: “Your brain is not an onion with a tiny reptile inside” (Cesario et al., 2020). The neuroscientist Luiz Pessoa showed that the so-called “emotional” and “cognitive” regions are so intertwined that it is hard to separate them (Pessoa, 2008).
In this guide we therefore use the familiar words (“limbic brain”, “alarm”, “cortex”), but as shortcuts for talking about systems that work together.
What are emotions for? Survival
From the point of view of evolution, emotions are preparation programmes: in a fraction of a second they direct attention, change the body (heart, breathing, muscles) and push towards a useful action in a situation that has recurred for millions of years.
A little theory · For the psychiatrist Randolph Nesse, natural selection shaped emotions because they helped our ancestors deal with typical situations: a danger, a loss, an injustice, an opportunity (Nesse, 1990; Nesse and Ellsworth, 2009). An emotion isn’t “good” or “bad”: it is more or less suited to the current situation.
The smoke detector principle
A smoke detector sometimes goes off because of burnt toast. It is annoying, but it is designed that way on purpose: failing to detect a real fire would cost far more than a false alarm. Our alarm system follows the same logic. For our ancestors, mistaking a branch for a snake cost almost nothing; mistaking a snake for a branch could cost them their life.
A little theory · Nesse calls this the “smoke detector principle”: when a defence (fear, nausea, pain) costs little and an undetected danger costs a great deal, natural selection favours a system that gives many false alarms (Nesse, 2005). It helps explain why anxiety goes off so often “for nothing”: the system isn’t broken, it is set to be cautious.
The fast alarm
When something looks like a danger, the information can reach the amygdala very quickly, even before you are aware of what you have seen. The body gets ready: the heart speeds up, breathing changes, muscles tense. At the same time, the information reaches the cortex, which analyses it in more detail and can confirm the alarm or put the brakes on it (“it was only the cat”).
A little theory · Joseph LeDoux described these defence circuits in animals and then in humans (LeDoux, 2000; Phelps and LeDoux, 2005). Today he insists on an important distinction: the survival circuits, which detect threat and prepare the body, are not the same as the conscious feeling of fear, which also depends on the cortex (LeDoux, 2012; LeDoux and Pine, 2016). That is why the body can react even when you “know” there is no danger.
The role of the cortex in survival
The cortex isn’t simply a “brake” placed on top of the emotions. It also plays an essential part in our survival:
- Predicting. The brain continually anticipates what is going to happen and what the body will need (energy, alertness, rest). An emotion is partly a prediction: “this looks like danger, get ready”.
- Anticipating and planning. Faced with a distant or merely possible threat, the prefrontal cortex lets us think, choose a strategy and avoid the danger in good time. It is our great advantage: we don’t only run away, we also plan ahead.
- Nuancing and regulating. It weighs up the context (“it’s a film”, “it’s a drill”) and modulates the alarm response. Techniques such as reappraisal in CBT, or naming what you feel, rely on this mechanism.
- Learning that the danger has passed. When a feared situation goes well, the prefrontal cortex records new learning (“I’m safe here”) that holds back the old fear.
- Living in groups. Understanding others’ intentions, cooperating, asking for help: for human beings, social bonds are a fundamental survival strategy.
A little theory · In an experiment in which a virtual “predator” chased the participants, brain activity shifted from the prefrontal cortex (distant threat: planning) to deep regions of the brainstem such as the periaqueductal grey (imminent threat: reacting) as the predator came closer (Mobbs et al., 2007; Mobbs et al., 2015).
A little theory · Reappraising a situation (“maybe it isn’t what I think”) activates regions of the prefrontal cortex and reduces activity in the amygdala (meta-analysis by Buhle et al., 2014; Ochsner and Gross, 2005). Simply putting an emotion into words also reduces the amygdala’s response (Lieberman et al., 2007).
A little theory · Fear extinction depends partly on the ventromedial prefrontal cortex: it isn’t about erasing the old fear, but about learning something new that competes with it (Milad and Quirk, 2012). This is the principle of gradual exposure in CBT (Craske et al., 2014).
The other side: a cortex that imagines dangers
Our ability to plan ahead comes at a price. An animal feels fear when the predator is in front of it; we can feel fear about an exam in three weeks’ time, about an illness we don’t have, or go over a past argument for hours. The cortex produces scenarios, and the alarm reacts to them almost as if they were real dangers. This is one of the sources of worry and rumination.
A little theory · The neuroscientist Lisa Feldman Barrett describes the brain as an organ that constantly predicts the body’s needs and the situations to come, based on past experience (Barrett and Simmons, 2015). When predictions of danger dominate, the body stays mobilised even when there is no real threat.
When the alarm takes over
Under intense stress, the prefrontal cortex works less well: we think less clearly, find it hard to concentrate, and fast reactions and habits take over. In real danger this is useful: better to jump aside than stop to think. But in an anxiety attack, an argument or an exam, it explains why “reasoning” doesn’t work at that moment.
A little theory · Amy Arnsten’s work shows that acute stress, especially when it feels uncontrollable, triggers a release of neurotransmitters (noradrenaline, dopamine) that quickly weakens the functioning of the prefrontal cortex and strengthens that of the amygdala and of habits (Arnsten, 2009). It is reversible once the stress subsides.
The psychiatrist Daniel Siegel offers a simple image, the “hand model”: when the alarm is too strong, it is as if the cortex “goes offline” (“flipping your lid”). It is a teaching metaphor, not an anatomical description, but it helps a great deal in understanding what happens.
What changes in practice
- Your emotions aren’t your enemies. They are trying to protect you, even if they sometimes aim at the wrong target (worksheet 76).
- When the alarm is very strong, calm your body first and think afterwards: slow breathing, a sigh, cold, movement, grounding (worksheets 15, 43, 79, 93). Trying to reason in the middle of the storm rarely works.
- Name what you feel: “I’m noticing fear”. It is simple and it helps (worksheet 75).
- When you are calmer, reappraise: what is really happening? What other explanations are there? (worksheet 11).
- Teach your alarm that some situations are safe, approaching them step by step instead of avoiding them (worksheet 69, with your psychologist).
- Get to know your window of tolerance: when you leave it, you know what to do to get back (worksheet 91).
Worth bearing in mind
- The brain is much more complex than these diagrams, and most neuroimaging studies show associations, not simple causes.
- “It’s my amygdala’s fault” isn’t a complete explanation: your history, your body, your environment and what you have learnt count just as much.
- Understanding these mechanisms helps you be more understanding with yourself. If the alarm goes off very often or very strongly, a psychologist can help you adjust it.
Watch: short videos
- Dr. Dan Siegel’s Hand Model of the Brain, Daniel Siegel explains his “hand model”.
The videos open on YouTube. They complement this guide and are no substitute for support.
Worksheets to practise
- 133 · My smoke detector · Recognising the false alarms of my protection system
- 134 · My two speeds · The body’s fast reaction and the cortex’s slower view
- 135 · When the alarm takes over · My plan for coming back when I “lose it”
- 76 · What are my emotions for? · Understanding the message of each emotion
- 75 · Naming my emotion · Breaking an emotion down to understand it better
- 06 · Understanding my anxiety · The cycle of trigger, thoughts, body, behaviours (psychoeducation)
- 11 · The traps of anxious thinking · Spotting the most common thinking errors
- 15 · Slow breathing · Slow breathing to accompany anxiety
- 43 · The calming sigh · A short breathing pattern with a long out-breath (cyclic sighing)
- 79 · Bringing the body’s intensity down (TIP) · Acting quickly on the body when emotion is extreme
- 93 · Coming back to the here and now · Grounding yourself when a memory intrudes
- 69 · Bringing on the sensations on purpose · Learning that the sensations of anxiety are not dangerous (interoceptive exposure)
- 91 · My window of tolerance · Noticing when I am over-activated, under-activated or in my zone
Sources
MacLean, P. D. (1990). The Triune Brain in Evolution: Role in Paleocerebral Functions. Plenum Press.
Cesario, J., Johnson, D. J. & Eisthen, H. L. (2020). Your brain is not an onion with a tiny reptile inside. Current Directions in Psychological Science, 29(3), 255-260.
LeDoux, J. E. (2000). Emotion circuits in the brain. Annual Review of Neuroscience, 23, 155-184.
LeDoux, J. (2012). Rethinking the emotional brain. Neuron, 73(4), 653-676.
LeDoux, J. E. & Pine, D. S. (2016). Using neuroscience to help understand fear and anxiety: A two-system framework. American Journal of Psychiatry, 173(11), 1083-1093.
Phelps, E. A. & LeDoux, J. E. (2005). Contributions of the amygdala to emotion processing: From animal models to human behavior. Neuron, 48(2), 175-187.
Pessoa, L. (2008). On the relationship between emotion and cognition. Nature Reviews Neuroscience, 9(2), 148-158.
Nesse, R. M. (1990). Evolutionary explanations of emotions. Human Nature, 1(3), 261-289.
Nesse, R. M. (2005). Natural selection and the regulation of defenses: A signal detection analysis of the smoke detector principle. Evolution and Human Behavior, 26(1), 88-105.
Nesse, R. M. & Ellsworth, P. C. (2009). Evolution, emotions, and emotional disorders. American Psychologist, 64(2), 129-139.
Mobbs, D., Petrovic, P., Marchant, J. L., Hassabis, D., Weiskopf, N., Seymour, B., Dolan, R. J. & Frith, C. D. (2007). When fear is near: Threat imminence elicits prefrontal-periaqueductal gray shifts in humans. Science, 317(5841), 1079-1083.
Mobbs, D., Hagan, C. C., Dalgleish, T., Silston, B. & Prévost, C. (2015). The ecology of human fear: Survival optimization and the nervous system. Frontiers in Neuroscience, 9, 55.
Barrett, L. F. & Simmons, W. K. (2015). Interoceptive predictions in the brain. Nature Reviews Neuroscience, 16(7), 419-429.
Arnsten, A. F. T. (2009). Stress signalling pathways that impair prefrontal cortex structure and function. Nature Reviews Neuroscience, 10(6), 410-422.
Ochsner, K. N. & Gross, J. J. (2005). The cognitive control of emotion. Trends in Cognitive Sciences, 9(5), 242-249.
Buhle, J. T., Silvers, J. A., Wager, T. D., Lopez, R., Onyemekwu, C., Kober, H., Weber, J. & Ochsner, K. N. (2014). Cognitive reappraisal of emotion: A meta-analysis of human neuroimaging studies. Cerebral Cortex, 24(11), 2981-2990.
Lieberman, M. D., Eisenberger, N. I., Crockett, M. J., Tom, S. M., Pfeifer, J. H. & Way, B. M. (2007). Putting feelings into words: Affect labeling disrupts amygdala activity in response to affective stimuli. Psychological Science, 18(5), 421-428.
Milad, M. R. & Quirk, G. J. (2012). Fear extinction as a model for translational neuroscience: Ten years of progress. Annual Review of Psychology, 63, 129-151.
Craske, M. G., Treanor, M., Conway, C. C., Zbozinek, T. & Vervliet, B. (2014). Maximizing exposure therapy: An inhibitory learning approach. Behaviour Research and Therapy, 58, 10-23.
These worksheets do not replace therapy. If you are in distress or having suicidal thoughts, call your local emergency number (112 in Europe; 3114 in France, free, 24/7).
