From heart-pounding jump scares to the shiver that runs down your spine, the human brain is hard wired to detect danger and prepare our bodies to respond. But what is triggering those goosebumps when we get scared, and why do some people actively seek out scary experiences?
For Halloween we asked HMRI Brain Health researcher Dr Jacqueline Iredale, and Finn Thomas from the University of Newcastle to break down the science behind fear and why sometimes being scared can be a treat.
Fear is one of our most basic human instincts and evolved to help us recognise and respond to potential threats.
“Fear initiates our fight or flight response, sometimes called the fight, flight or freeze response,” Dr Iredale explains. “It’s an involuntary reaction and survival mechanism that kicks in as a means of protection or defence against a form of danger, whether that’s real or perceived.”
The brain initiates a response, activating pathways that prepare the body for action.
“The amygdala rapidly evaluates sensory input for potential danger, the hypothalamus and brainstem trigger autonomic changes and the hypothalamic-pituitary-adrenal axis coordinates longer-term stress responses through cortisol secretion,” says Finn.
While all this is happening inside the brain, there are noticeable, physical reactions taking place too.
“Typically there’s an increase in heart rate, respiration rate and blood pressure, sweating, trembling, nausea, tightness in the chest or throat. We might be less able to think rationally, and some people can freeze or become immobile,” says Dr Iredale.
Essentially the body redirects energy towards immediate survival. These physical changes are designed to help us react quickly, even before we’ve fully processed what’s frightening us.
If your arm hairs stand up during a scary movie, there’s an evolutionary explanation.
When the brain detects a threat, adrenaline and noradrenaline trigger tiny muscles attached to our hair follicles to contract, producing goosebumps.
“This reflex, called piloerection, actually used to serve an important survival function in our fur-covered ancestors,” Finn says.
“It’s a leftover evolutionary response intended to make animals, typically furry, look larger and more intimidating to predators,” Dr Iredale adds.
Humans have retained this response, even though our relatively hairless skin makes it less useful as a defence mechanism.
The same response pathways can also produce a shiver down the spine, even when we’re not afraid. Finn explains that this sensation, known as frisson, can be triggered by strong emotions, which is why some people experience it while listening to particularly moving pieces of music or watching films.
If fear evolved to protect us, why do some people willingly watch horror films or pay to explore haunted houses?
Dr Iredale says the answer partly lies in knowing the threat isn’t real.
“In some instances, for example when you are consciously aware a threat isn’t real, the rush of adrenaline caused by fear can be enjoyable due to the overlap between feelings of fear and those of excitement.”
“For some people they seek the sense of relief that comes when the fear passes,” Dr Iredale says. “For others, watching horror movies can also be a safe way to explore darker or frightening ideas without the actual danger.”
Sometimes the brain’s ability to generate fear can produce what is colloquially known as a sleep paralysis demon.
Sleep paralysis occurs when someone becomes conscious while the temporary muscle paralysis associated with rapid-eye-movement (REM) sleep is still present. Dream-like imagery can persist as we wake, creating vivid hallucinations of shadowy figures or threatening presences.
“Because the body is immobilised and the mind is half-awake, the brain struggles to explain this mismatch between the sensed threat and the lack of motor response, leading it to construct a narrative,” Finn explains. “So, often it’s a hostile figure, shadow, or ‘demon’, that feels external and menacing.”
These experiences can feel intensely real, but they are just the brain’s attempt to make sense of being awake while elements of dreaming remain active.
This Halloween when a spooky sound makes your heart race or a costume-clad stranger makes you jump, remember that your brain is doing exactly what evolution designed it to do. It’s preparing you for danger, even when the scariest thing in the room is just someone in a costume.
