I am having a discussion with a friend trying to convince him that we do not use only %10 of our brains.

I am aware of the answer here as well as the Snopes and Wikipedia pages (which actually have the exact same answer), as well as various other sources.

Specifically, he has counter arguments to several points.

For the Localization of function, Brain Damage and Neural disease he makes the point that much of the brain may be necessary as some sort of messaging system without being used directly.

He dismissed the evolutionary argument as simply being a theory and for that particular argument (not evolution in general) lacking adequate evidence. I have tried explaining theory in a scientific context vs a layman context but that has not made a difference so far.

So finally he attacks the various brain imaging technologies as being too inaccurate to show the entire brain is used. In his words showing layers or various sections in use is not equivalent to showing the entire brain in use.

To clarify, these are not my arguments but I am looking for advice/empirical evidence that I can use to make my argument. I am not looking for personal advice or advice on how to deal with overly skeptical people....just for further evidence or sources, or explanations I can provide that show we do in fact use all of our brains.

Specifically, how precise/accurate is our various brain imaging technology? Is it capable of showing every cell or neuron in use at once? Is the technology we have able tt show we do use 100% of our brain, every part of our brain without question?

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    What do you mean with the word "use"? Specifically, if something is used as a messaging system, how can you say that it isn't used?
    – Christian
    Jun 5, 2011 at 14:35
  • I mean use for processing something as opposed to just being a relay. At this point I am just wondering to what extent we can show the brain is in use, regardless of how it is used. Jun 5, 2011 at 15:06
  • What evidence do you produce to convince someone that he should value evidence? Or, in other words, it is hard to use logic to talk someone out of a position he didn't use logic to arrive at in the first point.
    – Lagerbaer
    Jun 6, 2011 at 16:55
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    To resolve this debate/argument, it would probably be helpful to have your friend define what he considers "use" with regards to percentages of the brain. In other words, if the brain imaging technologies are "too inaccurate", what is accurate enough? The other side of this same coin: How does he know we only use 10%? How did he get his knowledge and is that empirical evidence any better than the evidence you have provided?
    – MrHen
    Jun 6, 2011 at 17:16
  • As you posit it, your friend debunks his own theory: if a part of the brain is needed as part of a messaging system, it is being used. Case closed argument over.
    – horatio
    Jun 7, 2011 at 15:34

3 Answers 3


The method generally used to observe which parts of the brain are currently active is functional magnetic resonance imaging (fMRI). Specifically the BOLD (Blood-oxygen-level dependence) is used to measure the blood oxygen level that is influenced by the energy used by active neurons.

The oxygenation state of haemoglobin influences the transverse relaxation rate of the water protons in blood (Thulborn et al., 1982). This transverse relaxation rate can be measured by MRI, and thereby the activity of the neurons in the brain can be observed.

The spatial resolution you can achieve with modern, high-field MRIs is about 1x1x3 mm3 (van der Zwaag et al., 2009). This is far larger than a neuron, so observing individual neurons inside the brain is not currently possible with this method.

This is of course an indirect measure of brain activity, you're measuring energy consumption, not the neural activity directly.

There have been thousands of studies performed using fMRI, if we used only 10% of our brain somebody would have noticed that. You could of course poke holes into that and argue the limitations of the current methods, but according to everything we currently know we use our whole brain.

I would not discount the supporting evidence so lightly, especially the fact that when you damage some part of the brain, it usually has a pretty dramatic effect on a person. We have pretty solid empirical evidence that all parts of our brain are doing something.

The part about messaging is also a strange argument. The main function of neurons is to pass electrical signals along, that is essentially "messaging". Arguing that this is "doing nothing" doesn't make much sense.

  • If we don't have the technology currently to show per neuron/cell then how can we actually know for sure? Surely at the moment it is just implied (with a lot of evidence to indicate it is true), especially if we only measure energy consumption and not actual usage/processing? Jun 5, 2011 at 15:38
  • @Sonny, we know nothing for sure. We just look for evidence that it is not true. That is how science works. Science is not a tool to prove things, but rather to disprove things.
    – picakhu
    Jun 5, 2011 at 16:13
  • @picakhu, yeah, I know. I should not have phrased my comment above as I did, but what was I trying to get at is that at the moment we don't have hard evidence showing we use all of our brains, just a huge amount of evidence implying it and a lot of well thought out logical arguments. Not questioning that we do, but was specifically looking for empirical evidence to show to my friend. Jun 5, 2011 at 18:29
  • @Sonny, The way science works, no amount of evidence can confirm any theories, it can just be support for the theories. In this context, it is possible that only 1 braincell is the actual brain and the rest light up at random, but the evidence shows that is not the case. That is what I meant.
    – picakhu
    Jun 5, 2011 at 18:34
  • @picakhu, I know how science works, thanks. The evidence we have does not show that all or even a majority of cells are used at once, as Fabian's answer states. Now, eventually as technology gets better it will show that, and that will be the empirical evidence I ask for in my question. Which is of course, quite a separate thing from proving or disproving any theory. Jun 5, 2011 at 20:48

To put this whole vague matter into a nutshell:

If something is in use, is working, it consumes energy. Point :)

So to answer your question i looked for changes of brain activity (sleep, resting, cognitive tasks...) and overall energy consumption of the brain. 2 very good articels putting your question into a bigger picture, quite academically written, but focus on the statements concerning energy consumption. The articels also discuss, what actually can be derived from brain imaging data (fMRI, PET), how higher conscious brain functions relate to physiological changes measured by these techniques.

The basic conclusion is, that the brain doesnt variate much its energy consumption, whether resting, tasked,...Contrary it needs a average high activity (high metabolism, energy consumption) to make specific functionality possible at all. So its not like a computer, where you start a program (analog higher conscious brain function, e.g. playin chess) and then processor and memory consume raise, the energy consumption is already and constantly on a high average level, otherwise the operating system (brain) couldnt run at all a distinct software (function).

quoted the to me most important parts, but both articles give pretty good overview and draw bigger picture around ur question.

brain represents about 2% of the body weight. Remarkably, despite its relatively small size, the brain accounts for about 20% of the oxygen and, hence, calories consumed by the body (1). This high rate of metabolism is remarkably constant despite widely varying mental and motoric activity

This should clearly indicate, that we use and need the brain pretty much from a evolutionary point of view

showing that the maximum values of oxygen consumption and spike frequency achieved during stimulation were approximately the same from both baselines (i.e., both levels of anesthesia). The authors assert that an overall level of ongoing activity must be achieved for a particular function to occur

This high metabolic activity is present when we are completely passive and resting as well as when we are observably doing something. Two lines of investigation have recently converged in their analysis on how this energy is being used. Both have focused on the metabolic requirements associated with glutamate signaling in the brain. This focus would seem reasonable, considering that greater than 80% of neurons are excitatory and greater than 90% of synapses release glutamate (6, 7). Attwell and Laughlin (8) have taken a bottom up modeling approach using extant data on the blowfly retina and the mammalian cerebral cortex. Estimates from their approach indicate that most of the energy used in the brain is required for the propagation of action potentials and for restoring postsynaptic ion fluxes after receptors have been stimulated by the neurotransmitter. In contrast, maintenance of the resting potential in neurons and glial cells accounts for less than 15% of the total energy consumption. Shulman and his colleagues (9, 10) in a very different approach using MRS in anesthetized rats have shown remarkably converging evidence that a very large fraction (≈80%) of the energy use in the brain is correlated with glutamate cycling and, hence, active signaling processes

An intriguing hypothesis has emerged that the responsiveness of neurons to changes in their input depends on a continuous, high-level but balanced input of both excitatory and inhibitory activity (for review, see ref. 29). Importantly, it is the balance between this continuous excitatory and inhibitory input that determines the gain or responsiveness of the neurons to correlations in their input. In this formulation, spontaneous ongoing activity becomes a critical enabling factor in the creation of functional connections within circuits responsible for specific behaviors. Furthermore, this correlation-induced functional connectivity can be modified without causing variations in the mean firing rates of the involved cells. As Salinas and Sejnowski have pointed out in their review (29), balanced neurons have rich dynamics and can react to external stimuli on effective timescales that are much smaller than the membrane time constant of a single neuron.

So, how might this relate to our analysis of the energy budget of the brain? It should be noted that most of the neurophysiology discussed above concerns synaptic activity at the input to neurons. Because the highest energy-demanding processes in the brain are centered at these sites (27, 28), it suggests that much of the ongoing or baseline metabolism is devoted to processes occurring there. We might therefore posit that, in the brain, a large majority of its metabolic activity is devoted to ongoing synaptic processes associated with maintaining a proper balance between excitatory and inhibitory activity. Maintenance of this balance allows neurons to respond appropriately to correlational changes in their input and establish the functional connectivity as required for a particular task.

Thus, we may entertain the possibility that the very high baseline or ongoing metabolic activity of the brain not only supports processes necessary for the maintenance of the proper responsiveness of neurons for the transient and ever changing functions of the brain but also instantiates a sustained functionality.


Indeed, relative to the high rate of ongoing or “basal” brain metabolism,6 the amount dedicated to task-evoked regional imaging signals is remarkably small (estimated to be less than 5%). The brain continuously expends a considerable amount of energy, even in the absence of a particular task (i.e., when a subject is awake and at rest). A significant fraction of the energy consumed by the brain (quite possibly the majority) has been shown to be a result of functionally significant spontaneous neuronal activity.7 From this cost-based analysis of brain functional activity, it seems reasonable to conclude that intrinsic activity may be as significant, if not more so, than evoked activity in terms of overall brain function.


So overall high average energy consumption of brain in conjunction with share of the total body energy consumption should make ur point very clear. Saying "but how often we actually use our conscious brain functions" is no counter argument, as the whole "software package" is needed, the brain doesnt behave as a multi-core cpu, its one big decentral core and software is consistently rewritten (e.g. dreaming, the brain doesnt deeply rest, when you sleep. Also some savants show ability to memorize immense amount of data when drawing conscious e.g. a detailed landscape they saw, while the picture saving with their eyes was a highly short & unconscious process, they dont see more than a average joe, they manage somehow unconscious to recall or save simply more information out of/in the brain)


Some paranormalist such as Dean Radin advocate a hypothesis according to which the brain is like a radio: The brain receives information via the senses. It sends the information through some kind of telepathic medium to the soul which isn't "in the brain". The soul in turn uses the same telepathic medium sends commands back to the brain. The brain then redirect those commands to various parts of the body to get the body to act.

fMRI measures brain activity indirectly through energy consumption. A radio that sends and receives commands does also consume energy.

When parts of the brain get damaged through brain surgery the mind stops working. A radio also stops working and plays crude sounds when you damage it.

At the present we don't have the ability to reconstruct a brain in a computer model to show that neuron activity is alone sufficient to explain the mind.

At present we don't have evidence that let's us reject the radio hypothesis. We haven't found any evidence that supports it either.

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    “At present we don't have evidence that let's us reject the radio hypothesis” – we also haven’t found any evidence rejecting the hypothesis that the brain works via a series of tubes operated by little green men that are invisible to microscope. In fact, this is more plausible than the radio theory, since that would violate the Dirac equation (and thus contradicts much of modern physics). In summary, I don’t see how this is relevant here. Jun 6, 2011 at 15:22
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    @Konrad: This is core of the issue about whether we "use" our brain of whether it's just a "messaging device". Maybe 10% of the brain do the "real thinking" and the rest plays radio.
    – Christian
    Jun 6, 2011 at 16:11
  • This is a Russel's Teapot hypothesis. It might make for an interesting thought experiment when you're shooting the breeze late at night with some friends, but it's entirely useless from a scientific standpoint. Feb 8, 2020 at 10:34

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