Why is Nibbanna unconditioned if it's dependent on mind & brain

Often it is said that nibbana is unconditioned, but nibbana is definitely dependent on other conditions. Also, according to modern psychology nothing can be 'eliminated' (greed, hatred and delusion in this case). Once learned, never able to unlearn. A skill, therefore zu can become either more efficient or less efficient, so why is it in Religion that something can be absolutely eliminated, whereas psychology tells us differently?