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.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%!