[bianca]

Experience lies embedded in the physical structure of the brain, in the neural connections and pathways, and the more we are exposed to stimuli, the more articulated these connections (and the wiser we are supposed to be). Wisdom is thus the product of experience through observing situations from different perspectives. Hallucinations aren't neural pathways in the brain, they are the brain's "perception of a nonexistent object or event" (wikipedia). They are caused under extreme stress, and lack of stimuli is one such example of stress, and a real torture at that. To survive, the brain will find a way to deal with the lack of stimuli by ... going awry. It builds up its own fictive pattern of stimuli and its own world. In other words, hallucinations do involve hearing, seeing, feeling, smelling and even tasting things, but these are not real. The brain believes it hears sounds, or feels the smell of something that is not there. This is (like many other mental disorders) a psychosis, a "loss of contact with reality". I don't know how these invented stimuli re-design the brain, or change its physical structure.

A sensory deprivation tank is per definition deprived of any sensorial stimuli and the only 'experience' one gets is that of nothingness, or void.

Myself, when exposed to less stimuli than I need (like monotony, or too much scilence, too little stimulance during a longer spell of time), I experience lack of concentration, of critical reflection, headaches and even apathy. But not everybody needs a lot of sensorial stimuli to live a normal life (there are introvert and extrovert people). Also, a child's brain is more malleable to experience / stimuli than an adult's.

I once read a book called "Raptor red" (which is about the world seen through the eyes of an animal) written by a paleonthology professor Robert Bakker, where a Utah Raptor watches a turtle and wonders what if its brain would be inside the turtle's head. The brain would get understimulated because the turtle's body is adapted to a monotonous lifestyle, just swimming around and doing the same thing every day. The raptor would get so bored that it would eventually die of apathy and boredom. Silence in the wildlife is never good, it is a sign of danger. If the turtle's brain would be inside the raptor's head, it would become so overstimulated that the turtle would soon withdraw, hide from the world, and wouldn't be able to function or survive. I deduce therefrom that the need for sensorial stimulance is individual for all the living creatures, and that deprivation of stimuli as well as overexposure to them can permanently limit a brain’s development, with all the consequences that this has for survival.