I’VE been thinking a lot about fear. For much of the last fortnight, a tiny interloper ensconced himself in the folds of my duvet. All parents know that when the breeze shivers curtains, and moonlight contorts the commonplace, our bed becomes refuge. To a child, it’s the safest place in the house. A night nose-to-nose with mum typically offers enough respite – but after three consecutive nights, I realised my son’s fear was something bigger that a solitary nightmare.

My children have cultivated an interest in being spooked. Point Horror, Goosebumps and a deep love of Neil Gaiman, and anything generally grisly or paranormal. When my eldest began enquiring about Freddy Krueger and Chucky, I thought Buffy a good compromise – family-friendly "mild peril" seemed like an intervention to stave off more googling. It quickly became an obsession. One that meant sneaking episodes in at night – with a little brother in the room. And so the bogeymen were identified: vampires. And with his nascent fear came an encyclopedic knowledge of the mythos that no amount of well-argued grown-up logic could attenuate the effects of.

Twenty-four years put enough distance between my own sleepless nights and his that I’d forgotten how ineffectual the reassurances of adults were. An episode of Michael Aspel’s Strange But True had engendered in me a deep phobia of alien abduction. It became a preoccupation – one that fuelled study of star maps, lunar phases, space flight and aircraft, all so I could maintain a vigilant watch of the night sky for anything untoward. “They don’t exist” did nothing to help.

Of course it didn’t. Rationale is a poor prescription for fear – our brain’s instinctive means of preservation. Exposure to perceived threat triggers an autonomic response, kick-starting a chain reaction that bypass conscious decision-making, to ensure our survival. From external stimuli, the thalamus relays messages to the sensory cortex for interpretation. This moves to the hippocampus for conscious memory retrieval and contextualisation of the stimuli. Next, to the amygdala, the brain’s Bletchley Park, to decrypt the threat, and bank the emotions for future use. Lastly, to the hypothalamus, and the triggering of the fight-or-flight response, firing up the sympathetic nervous system and the adrenal-cortical system. Stress hormones are dumped into the bloodstream, the nervous system switches to red alert. Muscles contract, blood pressure increases, our heart pounds, blood-glucose rises, pupils dilate, our lungs expand and our non-essential systems shut down. We are hardwired to be afraid – it’s what keeps us alive. Logic doesn’t stand a chance against such biological sophistication.

In the case of vampires and a child’s brain, what worked was employing a mental salve that worked with his fear – jotter-paper crosses taped to doors, a silver ring pinned to a pyjama top, an empty spray bottle filled with water and three garlic cloves. One night of restoring his sense of control, and he was back in his own bed sleeping soundly. Acknowledging how fear works allowed us to break the cycle.

When the brain is programmed to react with such asymmetry to threat, there is power to be found in manipulating this unconscious, atavistic process. Intimidation is a universal means of social control, cutting across species and stretching backwards through time. There’s ample evidence to suggest these behaviours aided our evolution. As a species we’ve advanced beyond competition for a mate as the ultimate social threat. We’ve constructed complex societies, fabricated borders, invented religions, developed weapons and taken to war as an inevitable means of asserting ourselves on the world stage – is it any wonder that we’ve consciously chosen to weaponise fear at this scale? From propaganda to terrorism, the perpetrators are puppeteers, yanking the strings of the most sophisticated bit of kit imaginable – our brains. Employing our own minds against us, using fear as a means of primal coercion.

Terrorists know that with little work, our brains will do the heavy lifting. They are but the agentic actors in mass-mobilised autonomic and cognitive response to threat – threat that governs our thoughts and behaviours. They know an act of senseless barbarism will produce an immediate response, inducing a state of fear that overcomes and controls the affected person, and will manipulate their perceptions in future. Thanks to global media, these acts can trigger a shift in perception far beyond those local to an attack.

Thanks to the media, we all remember September 11th. We all remember the 7/7 bombings. We all remember the Bataclan shootings, Charlie Hebdo, Nice and Westminster. And this ease of recall changes how we perceive threat. The Nobel Prize-winning psychologist Daniel Kahneman calls it the "availability heuristic" – a mental shortcut that allows us to make judgments about probability based on how easy it is to think of a similar example. The easier we can recall the consequences of an action, the more severe we interpret those consequences to be. So whilst the probability of finding ourselves or our loved ones caught up in an atrocity is slim, our ability to summon the devastation at will locks us into a state of fear, controlling how we interpret information and ultimately behave.

Terrorism works by turning our world against us. It speaks to our need to survive, recasting us as prey and our fellow citizens as predators. It makes our friends and neighbours into the shadows in the periphery, eliciting the chain reaction which leads to vilification, then used by extremists to vindicate their violent actions.

This is why business as usual is such a powerful act of defiance – a railing against the reptilian brain that terrorists rely on to keep us in a state of fear, and thus under control. When Parisians sat outside cafes smoking insouciantly into the night air, they sent a message. When Londoners continued to use tubes and buses, they sent a message. When Mancunians went to work, gigs, football games and stood together in the street singing, they sent a message: we’re not afraid. You don’t have that power. You will not make us victims of our own fears. It’s an example to all of us, and a powerful reminder that we won’t let the many be changed by the actions of the few.

Time and again we see terrorists try to sow the seeds of hate in the ground they’ve deliberately cultivated. But once again, in the wake of such horrors, we see those most deeply affected choosing to plant their own seeds: those of hope.