How many possible states does a brain have? Suppose I have a box, inside of which is a light which can be either on or off: it has exactly two states.
Suppose I wanted to take some "snapshot" of the state of this device, and store all the information about it, so that if I at some point had another device with sufficiently identical hardware + environment and a way of writing all the state to that device, I could recreate the state of that box.  There are n=two possible states (so it would require log2(n) = 1 bits to store the state).  

Now suppose my box is a brain.  To the nearest order of magnitude, how many possible states does the brain have?  

Assuming it's an adult human brain might make for the most useful answer to this question, but if you have more solid answers for brains of other animals while we wait on an answer for humans, feel free to post an answer stating that assumption.
2 2,752,000,000,000,000,000,000 states


  Disclaimer: This is obviously a very crude and imprecise estimation (in fact, it is ignoring some obvious parameters for the sake of simplicity). As Scott E. Page puts it: Even models that are far from accurate can teach us something.


If one considers the design of future artificial brain, you can make these rough assumptions:


A 32 bit floating point representation should suffice to capture synapse elasticity.
There are about 86 billion neurons in the brain. The connectivity of which can be represented by a square matrix of size 86 * 1018 (86 * 109 to the power of 2). Each connection is weighted, 32-bit float.


Resulting in 86 * 1018 * 32 bits =

2752000000000000000000 bits (2.75 sextillion).

These many bits result in these many states:

2 2752000000000000000000

or:



This obviously a very rough estimation - you don't account, for example, to membrane potential, although you can argue that discarding membrane potential while maintaining neural connectivity and synaptic strength should suffice to 'reignite' a frozen brain.

Perhaps more importantly, a network structure can be represented by a matrix, but more often is represented by a sparse matrix - no neuron is connected to all other neurons, I believe 1000 is the average and some sources state that there are about 1,000 trillion synaptic connections.