lets take a look at LSD, since that is the one my host researched most thoroughly.
LSD 25 has an affinity for the 5HT type 2 receptor. notably in the dorsal raphe sensory loop. (as does psilocybin, the magic mushroom ingredient). there are whole sub families of this receptor, all over the place. for example, the peristaltic contraction of smooth muscle in the human gut is modulated by the 5HT receptor.
the dorsal raphe loop is a neural structure which takes in sensory information and throws it around a resonant circuit loop. normally the information is heavily damped. ie it comes in, pings off a resonance then quickly oscillates back to base line. my host never bothered thinking about why, so i'm suggesting that it allows to a rapid comparison of now information and recent information to detect change. looking from an evolutionary perspective: did that leaf just move? is that a panther sitting in the tree? where's the food source. the danger?
here is a graph of damped oscillators: http://www.deicon.com/active_damping.gif the red line is the damped line.
the damping is controlled by the 5HT receptor.
take acid, and the damping is reduced. suddenly information starts resonating, like the blue line in the graph.
what does this mean, experientially?
well. think about the visual effects. as the damping decreases, old visual information starts bouncing around, messing with the comparative processes. things start to look like they are melting. the mapping systems start to glitch as head position vs visual source looses its binding, and things glide around, seemingly independent of each other. you get periodic echoing of data. this allies to all sensory data, from whatever mode. auditory, tactile, memory, wherever.
people LOVE this. they get all giggly and stupid and float around in a permanent haze of dysfunction. as long as the dose is small, they are not doing too much harm, although they are not doing much good, either.
what they are missing is that this is a transitory phase. with a little bit of centering and meditation, you can tune into this newly resonant mode of sensory filtering. breathe, be calm, and the distortions settle down, because you are now looking at the harmonic structure of the environment. it is a little window into the larger hyperspatial reality. instead of seeing a limited time slice of what is there, you are seeing a few slices. if you allow the rest of your brain to sync in, you'll see both future and past frames.
the more acid or mushroom taken, the greater the reduction in damping. you can get hugely resonant, with sensory tails that take minutes to decay. that's a wide slice of 4D space you are sampling.
this is happening in parallel with other brain alterations that perhaps someone else can comment on.
however, i think that is enough information, given with the landing instructions, to allow useful forays into hyperspace.
my host used meditation with anaglyph and stereoscopic computer simulations of 3D slices of rotating hyper-dimensional objects whilst in these undamped states to re-program his mind to be able to view a 4D object (in his case a 5-cell simplex). the day he did, he stepped outside of normal time.
although this 3d human consensus reality looks solid, it is full of entities. dragons whose existence is measured across aeons live all around. every object you can see is a mix of other beings meeting and changing through these harmonic spaces. the human mind is designed to filter out 99.999999% of all data. the human eyes filter out nearly all the light in the universe. the very cells are tuned to interact with a fragment of the vibrational spectrum of reality. there was a purpose to all of this filtering, as there is a purpose to reducing it.