<i>My argument is at atomic level, Heisenberg principle comes into picture and somehow stochastic nature is inbuilt into it.</i><p>Your argument applies more to CPUs than brains.<p>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 <i>as</i> 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.<p>So assuming neurons are what we think with, human thoughts are at least as deterministic as computer calculations.