Using 100% of your brain

The new movie Limitless is based on the premise that a drug can enable us to use “100% of our brains” because according to common wisdom, we currently only use 10%. This claim has been used in innumerable science fiction settings to provide a hypothetical source of magical cognitive abilities from super-intelligence to extra-sensory perception and is one of the most ill-informed and silly pretexts I’ve seen.  Of course, this realization is not new but I felt like writing a short rant.

The observation that we only use 10% of our brains comes from early brain scans where we observe that approximately 10% of our neurons are active at any given point in time. Of course what people fail to realize is what it would mean if every neuron was active. Professor Leslie Valiant of Harvard has done some nice work characterizing mathematically what the activity to inactivity ratio would have to be to optimize the information carrying capacity of a theoretical neural network. A trivial example will illustrate the point.

Let’s suppose that each active synapse represents a single bit. It represents 1 when it is actively transmitting an impulse train, and 0 otherwise. A brain state in this model is simply a collection of bits that encode motor routines, or parts of our memory such as a prototypical image of a cow and the associated moo sounds. Now if every neuron were active in this model, then the brain would be able to represent only a single state, all ones. Under this model, if 100% of our brain was active, we would be rendered completely inert. In fact epileptic seizures approximate this condition, a runaway cascade of activity that turns on a large fraction of our neurons and paralyzes the mind. Some cognitive science experiments are now performed by ‘turning off’ regions of our brain to explore their role in decision making, morale judgement, etc. A region is turned off by over-stimulating a region of our brain using magnets. The hyper-activity effectively paralyzes that region for short periods until normal functionality returns.

Marvin Minsky, one of the founders of AI, is fond of saying that we spend too much time looking at the traces of activity in brain imaging and that regions that are inactive may be just as important as those that are active. That is to say, if you are writing down a binary number, zeros are just as important as ones – the zeros space out the ones into more a sparser and more meaningful configuration.

What Leslie Valiant found is that the number of total possible states represented by a neural network is maximized at an activity level very similar to that observed empirically. So unfortunately for all those sci-fi writers out there, we are already making use of 100% of our brain’s capacity and anything that purports to increase the “activity level” of our brains would only serve to make us less capable. The premise behind Limitless, and many science fiction episodes like Stargate Atlantis’ “Tao of Rodney” is poorly conceived.

If we really want to become smarter, we will have to resort to the hard work of building more effective representations within the existing processing capabilities of our brain. Modern neuroscience backs me up here (e.g. summary in nice NPR interview); the process of compiling our experience into higher and higher order patterns that we use to structure future experience is what makes the judgement of experts more efficient than that of a novice (not always more effective, as the higher order patterns can also limit our generative abilities).

As we age these cognitive structure become richer and faster at integrating similar experiences into our existing knowledge base. The cost of this expertise is that it takes us longer to learn new things as we have to relate each new piece of knowledge to all the pieces that come before. Unfortunately, if we don’t stay limber, then we tend to lean towards discarding new items which don’t fit into the existing models. Aging gracefully requires a process of continually evolving and adapting these compiled models over time and having the guts and discipline to discard those that don’t support the new experiences we’re exposed to.  The new truth is that each year we learn more about how to think, and hopefully how to live.  The trick is not to get bogged down in the increased burden of mundane details that tends to come along with mid-life.

Anyway, here’s to making the most of our 10%!



  1. cnmcdee

    I do not fully agree. There are lots of ways to increase brain function with nootropics, with the website established to such research. I have taken them, and noticed marked improvements in tactile thought processes, focusing and in concentration.One of my favorite’s is L-HuperzineA a Chinese club moss, which is a Acetylcholerinase re-uptake inhibitor, and a second great one is Oxiracetam, and another is L-Tyrosine.

    • Ian Eslick

      I didn’t say we couldn’t increase brain function, but that increasing the percentage of the neurons that are firing at a point in time, within reason, is not the way to do it. At the neural level we can make changes such as speeding up the transition rates (and possibly frequency) of neuronal impulse trains, ensure sufficient neurotransmitters to avoid artificial scarcity of firing potential, etc. However, we cannot fire, simultaneously, a much percentage of our neurons on a regular basis without becoming less functional.

      In fact, drugs often make us feel smarter without increasing our measured performance. Even if they do give us a little improvement, like computer science, the most reliable way to improve cognitive performance is developing better algorithms, not faster processing speeds. There is really good data that you pretty significantly increase IQ by teaching students better heuristics (think “Stand and Deliver”, etc). I doubt you can get that magnitude of result by taking Chinese club moss or L-Tyrosine.

  2. Rarities

    Also im pretty sure in limitless using 100% of your brain was more of an analogy than the full truth. Referring to was cnmcdee said, it is possible to increase brain function and this being said; why couldn’t a person take a drug that completely changes their cognitive abilities and memory? and whos to say we just havnt found the correct combination of chemicals to create this effect

    • Ian Eslick

      I think using drugs to modify neural architecture is potentially very interesting. The challenge is that a drug almost always provides a gross, global effect on the brain and is unlikely to have more than modest changes in our cognitive architecture. I certainly don’t mean to say that drugs can’t help, but to counteract the “100%” of our brain myth which emerged from early brain imaging which showed that rough 10% of activity.

      Check out the work of Dabrowsky from the mid 1900’s on “giftedness”. One of his core hypotheses is that the trait that gifted people share is ‘over-excitabilities’. His theory is that the developing neural architecture of these people as children were heavily influenced by their unique adaptation to an oversensitivity of one or more of the senses. If you work with gifted people, particularly children, the prevalence of over-excitability (and other unusual mental or personal characteristics) is profoundly obvious. Scientifically this inference is weak, but practically I’ve found it a useful model – especially in helping smart people internalize that what makes them different from others is the root of what probably makes them smart.

      For example, what is remarkable about Genius is that it is a difference in kind, not degree. I’ve had the good fortune to work with a few true Geniuses over the years and while they are at the high end of the scale in terms of how quick they are or how well their memory works, it’s not that ability that sets them apart (I have also known many amazingly quick thinkers who were not Geniuses). Genius emerges from a profoundly different outlook or way of thinking that happens to be extremely functional in the area of study that person has dedicated themselves to. I’m sure there are many genius intellects who never found a canvas to which their unusual brains were appropriately suited.

      I sometimes wonder, wistfully, how many Mozarts, Beethovens, or Hendrixs have been born into poverty and never had the opportunity to see an instrument, let alone have the best tutors in the world starting at the age of four.

  3. Lanaya Bodrug

    Tao of Rodney didn’t use the 10% myth at all, it just said that there was more synaptic interaction between all the areas in Rodney’s brain, much higher than a normal person. That was because Rodney’s actual DNA was altered by an ancient’s machine. They had to use the same machine to reset his DNA. His brain wasn’t using more of itself, his brain was actually being forced to evolve.

  4. irfan Khan

    I totally agree to your…but who the hell was Einstein..does it fall in place to your so called 10 pc neuron perceived model!!!

    • Ian Eslick

      Intelligence is not correlated to the % of neurons activated, rather it is the way the activations evolve that predominantly drives what we typically call intelligence.

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