To expand on the "we only use 10% of our brains" myth: this probably started because we tend to actively use only a percentage of our brains at any given time. This doesn't mean that the rest goes unused, just that at some times certain areas of the brain are more active than others. The bizarre experiences caused by psychotropic drugs are not due to activation of some usually inactive or "locked" part of the brain, but usually due to inhibition or disinhibition of certain brain functions. For example, as I said before, there is a part of the brain that is responsible for letting you know where you ends and everything else begins. Many drugs can inhibit this function, resulting in the user feeling as one with the universe or god (this effect can also be recreated with electric stimulation, and can be the result of seizures). There are also natural inhibitory functions in the brain, i.e. it is the job of some parts of the brain to inhibit other parts of the brain depending on our state of consciousness. Inhibiting an inhibitory function can result in experiences like hallucinations, or hyper-vivid dreams, paranoia, etc. So while only 20 or 25% of our brains may be active at any given moment, every bit is used, and the consequences of disrupting the balance of inhibitory and active functions, having more of the brain functioning at once, is usually seizure.