Neurons fire depending on the impulses they get from other neurons. This seems to be 'deterministic'. However, sometimes it might be useful to use random processes instead. Does the human brain have built-in `random number generators' which influence its output?
Comparing this with a computer: when I make an algorithm, the computer will do exactly what it is told. But my computer also has a built-in hardware random number generator. I can use these random numbers for, say, a Monte Carlo simulation. Therefore, the computer is a combination of a `deterministic' machine and random number generators.
Finally, it seems that the only 'true' random number generators are quantum random number generators. However, a hardware number generator such as the one in my laptop is based on a chaotic system. Therefore, a very small change of a very small detail could already give a different result. Now there might be some random quantum process hidden somewhere in my laptop; the very small influence this has is then amplified by the chaotic system. Could this also happen in the brain?
