The art, science, and technologies of erotic pleasure have been developing within Terragen cultures for millennia, and in many parts of the Civilized Galaxy optimal or even maximal pleasure is considered a virtue.
Those sciences and technologies that are dedicated to art of pleasure are known as hedonics (various subdisciplines being erotogenics, erotocratic science, tantrayogics, hedonipharmicology, nanohedonics, and countless others). Hedonics can be as basic as simple animal coupling, eating, exercise, or other physical pleasures related to basic drives(always popular among near-baselines, splices, and other organic clades) or as abstract as sharing mathematical pornography, or endorphin cultivation through bionano-mediated neotaoist alchemics.
One of the most common applications of symbionics is the experience of seamless virched and virch/rl alternate realities, including a new infinite diversity of altered states and innovative perceptions and experiences. These may include mystical or ecstatic experiences of sublime or transcendental states of being, merging with other minds, and with higher toposophic entities or collectivities. While this may be undertaken for the purpose of spiritual development and the mystic quest, or the acquisition of knowledge for its own sake, most often it is for the purpose of enhanced or novel pleasurable experiences. Erotogenic, Biotantric (using bioborg wetware dni) and Technotantric states are all pursued, including sex or hedonic spirituality with minds of higher toposophic levels than ones own, or with neogenic dedicated erotogens created by such Minds for the enjoyment of sapients.
Of all the billions of neogenic species that have been created by terragen mindkind, a decent proportion are for the purpose of giving pleasure to other beings, or even to themselves or each other. The Erotogini or Erotogeni (sometimes called "touchies" "feelies" "shapies" or "moldies") are among the earliest of these, dating from the early interplanetary period, and over the centuries and millennia gave rise to so many daughter clades as to become a superclade in their own right. Many other species and clades have been created since, some using Erotogine templates and genomes, others completely novel. There are polities today, such as the Houses of Pleasure [Fantail Orbitals, Chios, Zoeific Biopolity] and the Hentai Orwoods [Jaysen, nominal NoCoZo] that have acquired tremendous wealth and prestige through the marketing of pleasure biont templates.
Nanoveau hallucinogens With the generation of new technologies, new ways to abuse them were bound to happen. Shortly before the Technocalypse the first of what became called 'Nanoveau hallucinogens' became available, according to the few remaining records. This blood-borne paste (i.e. - non-reproductive nanogen) became a very popular 'party drug' in the vein (pun intended) of LSD and Ecstasy.
The first nanoveau hallucinogen that we have significant records of appears to have been capable of accessing a human's blood stream via skin contact (leaving behind a telltale rash of microscopic lesions which lead to the particular strain's street name, 'Red Rush') and congregating inside the intracranial blood barrier. It apparently (no samples from the time still exist, but as indicated by autopsy & toxicology reports and extrapolations from other data) was able to zero in on activity in the optical center of the brain. After a brief (approx 5 minute from arrival) 'learn' period, it would pseudorandomly replay neural signals for the neuron it chose. In some beings, this cause catastrophic seizures, but in most it provided a 'cool' partial-perceptive replay of previous input. i.e. - a stop sign might be perceived as a red color on a later object, or an octagonal shape, or having white lettering across the middle, etc.
The more modern versions tend to have onboard databanks of 'artistic' sensory impressions, everything from the bliss-inducing 'White Cloud' to the adrenal-stimulating shock-tactic imagery of 'Splash' to the erotic 'T&A' series of nanoveau hallucinogens.
I think that "down" (like us) will eventually be considered a utility function of the brain: a good servant but a bad master. And a wide variety of "highs" will be in regular use, as appropriate for learning, social intercourse and inward exploration. The brain has its own alphabet, and we're all in the pre-literate era.
Mono, Focus, Grok, (various) ~ Increases the ability to concentrate on a subject.
Haze, Fadeout (Kanabinol, various) ~ Promotes unfocused free association and synaesthesia.
Pop, Kapow, Bonus (various nano) ~ Recognises and rewards certain types of behaviour with drug induced ecstasy.
Various neural (particularly the spinal reflex shunt) or physical accessories have made hedonic sex a very different experience from the primitive baseline act, but certain high-tech plagues such as have sometimes caused immunological problems.
For posthumans of certain societies being a nanocyborg opens up all sorts of possibilities for sexual pleasure, not available to entities who occupy more"invariable" forms. A couple of posthumans of any combination of the available sexes might choose to adopt nanocyborg bodies, or incorporate bionanotech which allows em to consciously shape and resculpt eir bodies entirely at will. Let's just assume for now that the couple's feelings for each other are not diminished, or changed for the worse, by eir breaking through a toposophic barrier.
With eir new polymorphic capabilities, ey can effortlessly craft fully functioning genitalia (both female and male, and not necessarily restricted to just one species) anywhere, out of any part of eir bodies, and give each other pleasure every which way imaginable. This gives new meaning to the term "multiple orgasms." With each set of genitalia, one can experience orgasm separately, limited only by the number one can form, and one's capacity for ecstasy. Separate nanocyborgs can merge with each other and repeatedly reform differently, experiencing orgasm in every cell-sized unit of eir polymorphic bodies.
Image from Bernd Helfert
Hedonistic Display, Moodomorphics
The everyday use of hedonistic technology and pharmacology (pharm) can cause problems in a social context, where it has become useful for people using the same types of pharm or hedonic tech to be able to identify each other, or for non users to be aware of their states of mind. It became fashionable early on to wear masks and costumes, like the Comedia del Arte or Mardi Gras of Old Earth, to indicate at first sight what mode of consciousness the revellers were in.. (Anything but having to explain where eir head is at.)
Other solutions include illuminated or message bearing jewelry or tattoos (see Clade Scrabo Prior), or moodomorphic clothing which was capable of changing into a fantastic but specific display mode when hedonics were being utilised. Moodomorphism was eventually extended to actually morph the whole body of the hedonics user (using genetic tweaking or bionano augments). Thus the various nearbaseline human species began to approach the flamboyant displays of birds.
While the Dominion, the Biopolity and the TRHN are all for moodomorphics, stricter and more puritanical Negentropist elements see it as an appallingly wasteful way of subliminal/non-vocal communication.
Ad-Drugs - Text by Todd Drashner Pharmaceutical advertising; a class of tailored drugs which are either supplied as part of a promotion for a particular product or stimulate a desire to purchase or obtain that product.
Andromorph - Text by M. Alan Kazlev Male-only erotorganic, usually a hu-animal splice (bull, stallion, etc.) with heavily erotoginized genome, exaggerated primary and secondary sexual characteristics, and exceptional sexual performance. Often used as a companion-sentient or in the sex-trade. In less civilized parts of the galaxy, may be referred to as a boydoll or toyboy (or worse). c.f. gynamorph.
Biotics - Text by Anders Sandberg Biotic drugs consist of genetically modified living plants or animals that are consumed to provide the effect of pharmaceuticals.
Dionysan Erotocracy - Text by Anders Sandberg Subversive hedonic movement that developed on Dionysos from the 16th and 17th centuries onwards. Emphasised erotic love, desire and pleasure as tguiding principles. Used social experiment, erotogenic neogens, drugs, tantric practices, and virches and literature. Although the original Erotocracy was relatively short lived and (at first) isolated to a few star systems, and proved not to be workable in its original form, it had a wide-ranging effect on other polities and societies throughout the Terragen sphere.
Erotogen - Text by M. Alan Kazlev with additions by Anders Sandberg and Tony Jones A neogenic clade optimised for a highly diverse and voracious sexual lifestyle, known for how they physically and psychologically adapt themselves to their current partner(s).
Festival of Sin (SinFest) - Text by Ryan_b Hedonic festival also known as the Seven Deadly Days and Get Krek'd Week. Originating from the Amantus system it is a popular and extreme celebration of pleasure.
Gynamorph - Text by M. Alan Kazlev Female-only erotorganic, usually a hu-animal splice (cat, bird, rabbit, etc.) with heavily exaggerated primary and secondary sexual characteristics and exceptional sexual performance. Often used as a companion-sentient or in the sex-trade. In less civilized parts of the galaxy, may be referred to as a girldoll or toygirl (or worse). c.f. andromorph
Marijuana - Text by Kirran Lochhead Strang A herbaceous plant from Old Earth in the genus Cannabis, known as a source of psychoactive chemicals. Although once widely considered a very harmful drug, and outlawed, marijuana was eventually made more legal than tobacco in many polities, though later such laws became either irrelevant or unenforceable due to the rise of DNI mediated drugware and easy 'natural' drug production at home.
Narco-Symbiont - Text by Mike Parisi Also known as Naco-Sym or NarSym. Any small gengineered life form, which affixes itself to a subject's body, and supplies em with small, regular amounts of endorphins or some other pleasure-inducing substance.
Narcotic Programs (Narcograms) - Text by Ryan B Psychoactive Neural Interfacing: software protocols designed to operate via a biont's DNI or a vec/virtual's processor to generate recreational psychoactive effects.
Nootropics - Text by Ryan B Any chemical that can boost the biont brain performance or a cognition-enhancing drug that has no significant side effects. Also called smart drugs because of their ability to enhance brain's functions.
Other Self - Text by M. Alan Kazlev Bionano wetware consisting of drugs and bionanites that causes temporary personality alteration.
Pourmurmide - Text by Anders Sandberg A nanodevice-drug that rewires the brain of the recipient to experience every situation as meaningful and filled with spiritual power. Persons under the influence of pourmurmide will be quite incapable of acting on their own in society, since any course of action is seen as totally fulfilling, meaningful and destined.
Rat Barrel, The - Text by Peter Kisner; updated by Steve Bowers Originally an Interplanetary Age genetics research station, known as the Barrel, located at the Earth/Sun L4 position, far from any regulatory interference. The most common species of Rat Provolve, Rattus sapiens, was produced here in 410 AT, as well as many other species. Now a centre of hedonic drug manufacture.
Shopping Festivals - Text by M. Alan Kazlev A common type of corporate sponsored or encouraged festival in many regions. The NoCoZo celebrates the ancient rites of shopping festivals like xmas with gusto.
Smart Drug - Text by M. Alan Kazlev  A nootropic, a drug that enhances the functioning of the terragen central nervous system.  A programmable nano-drug, usually customisable, may enhance or alter consciousness or have other purposes.
Symbionic - Text by Glenn F. Cartwright Possessing a direct, neural interface between the brain and the environment Symbionics developed during the later information and early interplanetary periods, and for the first time allowed the biont mind to directly channel wireless, virtual reality information directly to the cortex, bypassing conventional sensory channels. This enabled complete and seamless virch participation, and virch realities that for the first time were indistinguishable from physical (rl) reality.
Tobacco - Text by Anders Sandberg The prepared leaves of the Old Earth tobacco plant Nicotiniana tabacam, used by Terragenmammals as a drug. The active substance is nicotine, a cholinergic agonist with mild mood and cognition enhancing effects and strong addiction potential. The drug is commonly smoked or chewed.