My argument is at atomic level, Heisenberg principle comes into picture and somehow stochastic nature is inbuilt into it.Your argument applies more to CPUs than brains.
Like with neurons, transistors in a modern CPU signal each other with pulses of charged particles. In both cases, the motion of those messenger particles is stochastic; it is primarily determined by diffusion due to concentration gradients (with transistors, the E-field as as important, but not more). Thermal electrons move a lot faster than small organic molecules, though, so there is correspondingly more quantum uncertainty about their position.
So assuming neurons are what we think with, human thoughts are at least as deterministic as computer calculations.
