Why do some people love spice, while others hate it? That is the question at the centre of a Chinese-American study into how our expectations alter the way our brains respond to sources of pain.
Capsaicin, the active component of chilli, can stimulate pain receptors on the human tongue.
But responses to this can be poles apart, which has puzzled scientists.
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The new study shows that positive expectations can reduce the perceived intensity of spice and increase enjoyment, while negative expectations can worsen feelings of discomfort or pain.
“Expectations shape our perception, profoundly influencing how we interpret the world,” the researchers wrote in a paper published in peer-reviewed journal PLOS Biology on Tuesday.
“Positive expectations about sensory stimuli can alleviate distress and reduce pain (eg placebo effect), while negative expectations may heighten anxiety and exacerbate pain (eg nocebo effect),” the team from East China Normal University, Virginia Tech, University of California, Berkeley and Wake Forest University School of Medicine wrote.
Recent studies had indicated that expectations could modulate sensory and emotional responses, including activation of the endogenous opioid, reward and descending pain modulatory systems, the team wrote.
To investigate the impact of “hedonic expectations” – or beliefs about the anticipated like or dislike of a stimulus – on a subjective experience, the team decided to examine neurobehavioural responses to hot sauce among study participants.
“I was intrigued by how people experience the same physical sensation in contrasting ways. Some, like myself, love spicy food, while others find it painful and hard to tolerate,” lead author Yi Luo, an investigator at East China Normal University, said in an interview with the journal.
“This made spicy food a unique and controlled way to explore how expectations and preferences shape pain perception.”
Participants who either “liked” or “disliked” spicy flavours were given high or low intensity hot sauce – or water – and asked to continuously rate their sensory experience, such as how “spicy” their mouths felt and how much they enjoyed the taste.
With the participants under functional magnetic resonance imaging (fMRI), the team did two rounds of testing to show how visually cueing spice levels affected participant ratings.
The researchers found that patients with positive expectations for spice exhibited more activity in parts of the brain associated with the placebo effect and “pleasure signatures”, whereas those with negative expectations had more brain activity associated with pain signatures.
“I was surprised by how strongly negative expectations amplified the brain’s pain response, even though the stimulus was the same. This highlights how our anticipation of discomfort can significantly intensify the experience of pain,” Luo said.
“These findings demonstrate that hedonic aspects of one’s expectations asymmetrically shape how the brain processes sensory input and associated behavioural reports of one’s subjective experiences of intensity, pleasure and pain,” the team wrote.
In the first round of testing, the participants were given neutral cues that did not indicate the spice level of the liquid they were about to receive. In the second round, they were shown colour-coded visual cues of the spice levels.
“Presenting the neutral cue run before the intensity cue run was strategically chosen to establish a baseline response to the neutral cue before introducing the potential interference or contamination from intensity cues,” the team wrote.
“In people who preferred the spicy sauces, the subjective experience of spiciness intensity changed after simply observing a predictive visual cue that generated an expectation of capsaicin intensity”, and led to increased activity in pleasure-related areas in the brain, the researchers said.
While the visual cues did not affect the subjective rating of intensity for those who disliked spice, it did decrease their rating of pleasantness of the sauce.
“Together, our results show that even when the sensory experience is the same, hedonic expectations modulate people’s conscious reports of their subjective experiences,” the team wrote.
“I hope this study encourages further exploration into how expectations shape our sensory experiences, potentially informing strategies for managing pain and enhancing therapeutic outcomes,” Luo said.
“I’m interested in exploring how cultural and individual differences in food preferences might influence the expectation effects we observed, potentially uncovering new ways to personalise pain management strategies based on someone’s unique background and experiences.”
More from South China Morning Post:
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