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I was looking for an answer to this question on the tubes and I was amazed to discover an impressive set of completely crap answers to this question.

Mesmerizing
Photo by kayaker1204. Creative Common License.

After a long search, the closest I could find to an answer is the following claim (by coincidence similar to my previous question)

Actually, the ancient Greeks noted the effects of visual flicker as early as 125 AD. They noticed that people often began to daydream or get sleepy when sitting around a flickering fire. This phenomenon is still true today. Since the flicker rate of fire light is rather slow, when you gaze in to a flickering fire, your brain activity tends to slow. This is why you might find yourself relaxing or even yawning around a kindling camp fire or a cozy fireplace.
source

Question: Is this claim backed by real science?

Bonus Question: Is there any scientific explanation to why fires are mesmerizing?

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  • You must have posted this while I was still writing my SHC question. Perhaps great minds do think alike ;) Apr 27, 2011 at 20:56
  • @Monkey: I was actually thinking about the BBQ I did today... :-P
    – Sklivvz
    Apr 27, 2011 at 21:13
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    Cheap guess: Evolutionary psychology.
    – Lagerbaer
    Apr 27, 2011 at 21:46
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    The old wives tale I heard is that sleepiness/yawning near a campfire is caused by decreased oxygen levels.
    – John Lyon
    May 5, 2011 at 4:28
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    The neuroscientist in me says you should probably better define "slow brain activity"...
    – nico
    Oct 15, 2011 at 12:24

2 Answers 2

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No, staring at a flame will not slow brain activity.

First of all, let's define brain activity, and see what 'slow' would mean in this context.

I had a lot of trouble finding a source that's neither completely technical nor completely nonsensical. In the end I opted for a combination of the two. Here is a semi-nonsensical one from which I am quoting the good parts:

Neurons communicate with each other by electrical changes. We can actually see these electrical changes in the form of brain waves as shown in an EEG (electroencephalogram). Brain waves are measured in cycles per second (Hertz; Hz is the short form). We also talk about the "frequency" of brain wave activity. The lower the number of Hz, the slower the brain activity or the slower the frequency of the activity.

Therefore, neurons discharge at a certain rate, and we can measure this discharge rate (notably, a lot of neurons have to discharge simultaneously for us to pick it up). This happens pretty quickly, and is expressed in how many times per second a group of neurons discharges. When measured by EEG, it comes out as a wavy line on the screen; hence the concept of brain waves.

On to slow and fast brain waves:

Researchers in the 1930's and 40's identified several different types of brain waves. Traditionally, these fall into 4 types:

  • Delta waves (below 4 hz) occur during sleep

  • Theta waves (4-7 hz) are associated with sleep, deep relaxation (like hypnotic relaxation), and visualization

  • Alpha waves (8-12 hz) occur when we are relaxed and calm

  • Beta waves (13-38 hz) occur when we are actively thinking, problem-solving, etc.

Since these original studies, other types of brainwaves have been identified.

  • The Sensory motor rhythm (or SMR; around 14 hz) was originally discovered to prevent seizure activity in cats.

  • Gamma brain waves (40-100 hz) are involved in higher mental activity and consolidation of information.

So, neurons discharge at different rates, and these rates are associated to different brain states. The ones of interest to us right now are the alpha and the gamma waves, because they are typically connected to activity in the visual system.

Relative to each other, alpha waves are slow (they happen when neurons discharge about 10 times per second), and gamma waves are fast (they happen when neurons discharge about 40-70 times per second, though even faster ones have been described).

So, to redefine your question a bit, when staring at a flame, one could say that we are in a slow brain state if we can find evidence of alpha waves, and a fast brain state if we can find evidence of gamma waves. The question is, which state are we going to find?

The answer is: gamma. Fast waves.

From a Nature paper:

In visual areas, attended stimuli induce enhanced responses and an improved synchronization of rhythmic neuronal activity in the gamma frequency band (40–70 Hz)

From the European Journal of Neuroscience:

During voluntary orienting of attention, we found alpha-synchronization to dominate over desynchronization, to be topographically specific for each of eight attention positions, and to occur over areas processing unattended space in a retinotopically organized pattern. This indicates that alpha-synchronization is an important component of selective attention, serving active suppression of unattended positions during visual spatial orienting.

Put together, these two quotes mean the following: an attended visual stimulus is connected to increased fast/gamma activity, while pulling attention away from a visual stimulus is connected to increased slow/alpha activity. Pulling attention away is typically done my making people stare at a spot where nothing is happening.

So, if you look at a fire, your visual brain will be displaying fast activity. If you look away from the fire at a place where nothing much is happening, your visual brain will go into a slower state. Looking at a fire does not slow brain activity.

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    What's a 39hz brain wave then?
    – Laurel
    Jul 1, 2023 at 1:59
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We know from studies that repetitive visual stimuli can cause a brainwave entrainment effect.

Modification of Brain Oscillations via Rhythmic Light Stimulation Provides Evidence for Entrainment but Not for Superposition of Event-Related Responses

Evaluating the entrainment of the alpha rhythm during stroboscopic flash stimulation by means of coherence analysis

If you look into the flicker rate of fire, the truth is that it is variable. However, several people have measured flames flickering in the 10 to 12 hz range, including Frequency and Phase Characteristics of Candle Flame Oscillation. This is at the high end of alpha wave range.

One of the known and most discussed benefits of alpha waves is that the promote relaxation and relate to a meditative state.

The Impact of Different Sounds on Stress Level in the Context of EEG, Cardiac Measures and Subjective Stress Level: A Pilot Study

Assuming sometimes they flicker faster, and sometimes slower, and depending on how relaxed or agitated you were before you sat down at the fire, I would say that yes, in many cases the flicker of flames will cause the predominant brainwaves to become slower - dropping from beta (standard waking awareness) into alpha (meditation and relaxation).

Since the entire phenomenon of light flickering inducing brainwave entrainment effects has been called into question, here are some of the studies.

The article titled "Optimal flickering light stimulation for entraining gamma waves in the human brain" published in Scientific Reports discusses the potential of flickering light stimulation as a non-invasive intervention for Alzheimer's disease (AD) 1. The study found that gamma waves entrained by 40 Hz flickering light decreased beta-amyloid burden in the visual cortex of AD mice.

Nature.com. (2021). Optimal flickering light stimulation for entraining gamma waves in the human brain. https://www.nature.com/articles/s41598-021-95550-1

Another study titled "40 Hz Light Flicker Alters Human Brain Electroencephalography Microstates and Complexity Implicated in Brain Diseases" explores the impact of 40 Hz light flicker on human brain electroencephalography (EEG) microstates and complexity 2. The research investigates the association between 40 Hz light flicker and brain diseases.

PubMed. (2021). 40 Hz Light Flicker Alters Human Brain Electroencephalography Microstates and Complexity Implicated in Brain Diseases. https://pubmed.ncbi.nlm.nih.gov/34966258/

In a study examining the spectral Granger causality of entrained gamma EEG using flickering light stimulus, changes in gamma wave connections between EEG electrodes were observed 3. The study analyzes the strength of occipitoparietal to frontotemporal gamma wave connections and their statistical significance.

PubMed. (2021). Optimal flickering light stimulation for entraining gamma waves in the human brain. https://pubmed.ncbi.nlm.nih.gov/34376723/

The article "Optimal flickering light stimulation for entraining gamma rhythms in older adults" published in Scientific Reports suggests that flickering light stimulation at 40 Hz can entrain gamma rhythms and improve cognition in Alzheimer's disease patients 4. The research highlights the influence of luminance intensity, color, and flickering frequency on the efficacy of gamma entrainment.

Nature.com. (2022). Optimal flickering light stimulation for entraining gamma rhythms in older adults. https://www.nature.com/articles/s41598-022-19464-2

For those who said they don't want to bother reading the studies, the summary of this is... flickering light can cause a brainwave entrainment effect.

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    "We know that repetitive visual stimuli can cause a brainwave entrainment effect." Do we? Let's accept for the moment that flames can flicker at a similar frequency as alpha waves. You'll need to show this affects the brain, and that the effect is to produce alpha waves in sync with the flames.
    – Schwern
    Jun 30, 2023 at 15:20
  • Welcome to Skeptics! Please provide some references to support your claims. You have a citation to show that a particular set of arrangements of candles tends to show periodic oscillation, but nothing to show that it has an effect on brain activity. "I would say" is not strong enough evidence for an answer here.
    – Oddthinking
    Jun 30, 2023 at 18:20
  • I've edited this with some research to support what I'm saying. And, still, I would say that based on the research, the flicker of flames could cause an effect. I say it that way because I'm extrapolating from known entities- but as far as I can tell there has never been a study to directly prove this, so it is just that - a claim I'm making based on what I know. Jun 30, 2023 at 22:45
  • Thanks for the improvements, @JustinHandley. I am a little dubious about the first study (and its journal: Evidence-based Complementary and Alternative Medicine). They talk about "light", but the near-infrared LEDs where shone onto the bottom of the subject's palms. It isn't at all clear what mechanism might make flashing dim lights into one's flesh trigger different brain states.
    – Oddthinking
    Jul 1, 2023 at 10:16
  • So, I've gone ahead and replaced the first study one more time with this one: ncbi.nlm.nih.gov/pmc/articles/PMC4737907 - which is the one referenced by Wikipedia in relationship to brainwave entrainment to pulsing light. I apologize for the lack of research up front, I didn't know that the whole concept of brainwave entrainment was being called into question here. Since entrainment was assumed by the references in the original article and never questioned, I was just pointing out that their study references to gamma entrainment just showed a lack of understanding of entrainment. Jul 1, 2023 at 19:24

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