How many possible states does a brain have?
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.