Because of its proximity of the Dream Realms, a large portion of the Astral Plane is responsive to the will and desire of both astral and physical visitors, and can be shaped into matter and energy. More than a century ago, mages discovered this malleable area; in the ensuing decades they have learned how to use its special properties and have turned it into the vast magical construct known as Cerebrospace ("C-space" for short).
The original benefit of C-space was that its malleable but stable nature allowed information -- particularly magical information such as spell formulae -- to be "imprinted" on it. Such imprints were permanent until changed. Having experienced the loss of knowledge and information from the aftermath of Devastor, the discoverers of Cerebrospace lost no time in transferring vast quantities of magical and mundane data to C-space, where it could be consulted by all; C-space's first function, then, was as a massive extradimensional library. That function continues to this day, as many mages have made it a personal goal to preserve for future generations all the knowledge that they can find.
A strange behavior was observed from the beginning of C-space information storage -- when data was imprinted on C-space, structures formed around that data, mimicking media that the mages were familiar with. For example, when a mage transferred knowledge into raw C-space, it would manifest a solid, readable book. It was theorized that the human mind could not conceive of information without a medium to carry it, and that the mage's own subconscious actually shaped a familar medium around the abstract data. This was later overcome by cerebromagi who learned to recognize the very fabric of C-space as a medium in its own right, but the immediate benefit was the realization that material structures could be created through force of will and visualization.
This led to an explosion of "Cerebrospace colonization". Mages began to stake out "territories" and create fortresses and strongholds in C-space, and many tried to dwell there on a permanent basis. However, they soon discovered two things.
One was that C-space was not hospitable to living creatures on a long-term basis. Food created in C-space proved as unnourishing as illusionary food, despite its solidity.
Worse yet, though, was the discovery that even with imports of food from the Material Plane, mages who tried to live permenantly in C-space found themselves subject to a degenerative wasting disease. More than a dozen cerebromagi died before the danger was realized, and even now, there are those who think they can avoid the disease, which the Order of Physick dubbed CDS -- Cerebrospatial Degenerative Syndrome.
Decades of use have shown that mages may enter C-space for up to three weeks at a time with no ill effects. However, Cerebrospatial Degenerative Syndrome (CDS) will set in after three weeks in C-space.
Symptoms of early CDS are facial tics and occasional weakness in the limbs. In the intermediate stages, the mage suffers from paranoia, mania and other detrimental mental effects as the organization of his mind begins to break down. One unfortunate side effect of this is that sufferers rarely heed the advice of friends to leave C-space. Advanced CDS is denoted by loss of physical strength and great difficulty both breathing and thinking, progressively increasing until the mage dies.
Researchers from The Order of Physick theorize that the influence of the Dream Realms that makes C-space so useful also causes CDS by breaking down the orderly functioning of the nervous system. The disease can be cured any time before the sixth month simply by returning to the Material Plane for at least four weeks. Beyond sixth months' exposure, though, the condition becomes permanent and degenerative, and resistant to all attempts at healing, both magical and mundane. The best that mage-healers have managed so far is to prolong the life of a sufferer without alleviating the condition at all.
The other thing that the early colonizers of C-space found was that their strongholds and fortresses were only as effective as they themselves were; if an attacker were more skilled in the manipulation of C-space, he could easily penetrate or even dissolve the walls and gates preventing his access. A cerebromage could not count on a static object like a fortress remaining undisturbed in the face of someone determined to bypass it -- unless he were physically present and reinforcing it.
However, it was soon discovered that active constructs could be created that could defend the more vulnerable static constructs. Essentially golems made of the stuff of C-space using the various Create spells, these creatures could be imbued with a semblance of will and skill via the Initiative spell, and could substitute for their creators in the constant defense of their "territory". Plundering and raids of one cerebromage by another dwindled to a trickle after this discovery. (Some cerebromages have speculated, by the way, that the ability to create protective golems implies that much more is possible, including perhaps even copying a human mind into the fabric of C-space; no few mages are pursuing researches into the possibilities of the plane.)
Cerebrospace has one other quality of use to mages. It is a very high mana zone, and magic can be used by anyone who physically enters it. Those visiting astrally cannot use magic in C-space, though.
Today, much of C-space is an open and friendly area. Some altruistic mages have set up libraries and facilities open to any who would use them, while others guard their territories jealously. The artistic urges of many mages find expression in C-space, populating this once-barren zone with all manner of creations, from forests and castles to abstract geometric shapes and palaces of light and air. Later generations of cerebromages seem less inclined to pay attention to the conventions of the Material Plane when building in C-space, and as a result, the structures and creations found there are increasingly breathtaking and otherworldly. Many mages spend time there as much to enjoy the beauty that others are creating as to make use of its unique resources
A number of spells from the Gate College (found in GURPS Grimoire) are required to make use of Cerebrospace. As noted therein, these are individual spells that must be learned separately from other variants.
Planar Visit: One version of this Gate College spell can be used to enter C-space in a spirit form. While there, the subject of the spell may read any unguarded data, or data which he is explicitly given permission to read by someone physically in C-space. The subject cannot enter areas of C-space that are "protected" or "walled off" to prevent unwelcome guests.
Planar visitors are visible in C-space, but their nature is obvious from their misty and ghostlike appearance. Persons and constructs in C-space can communicate with planar visitors without any penalties except for those imposed by language.
Plane Shift: This spell has a version that allows the caster to physically enter Cerebrospace. Fatigue cost to enter C-space is 20.
Create Gate: Used to open a gateway into Cerebrospace, or from it back to the Material Plane. Cost for a temporary gateway lasting 1 minute is 200 Fatigue.
There are no natural gates into C-space, and cerebromagi are reluctant to build permanent ones. Those that have been built are usually keyed to their creator, who must open the gate himself and (frequently) accompany anyone who passes through it.
Create Servant/Create Warrior/Initiative: These spells are used to create the active constructs needed to preserve and guard a mage's C-space structures. The Initiative spell (from GURPS Grimoire) is used to give such creatures independence and the Manipulate Cerebrospace skill (below), rendering them complete. The Create spell builds these creatures from the fabric of C- Space, so they may be either dispelled with magic, or Manipulated out of existence. However, in any such attack, they always resist with the greater of either their Power (the level of the Create spell used to make them) or their Manipulate Cerebrospace skill, no matter which method is used against them.
Users of C-Space make use of the following skills:
Area Knowledge (Cerebrospace): This one is obvious.
Survival (Cerebrospace): This Survival variant is similar to Urban survival; it includes knowledge of whom not to cross, where you can go for shelter, and most importantly, how to recognize symptoms of CDS. This skill, while it has no formal prerequisites, cannot be learned above a level of 12 unless the character has actually been in C-space.
Manipulate Cerebrospace (M/VH) Defaults to Will (not IQ) -6
Prerequisites: Survival (Cerebrospace), and either Plane Shift (Cerebrospace) or Create Gate (Cerebrospace) spell.
This skill is the ability to manipulate the fabric of Cerebrospace. This is used in many ways, the most common of which include the placement of data for storage, the creation of C-space constructs, and the subversion of another's constructs.
When used for creation, the user's level in this skill becomes a Power rating for the created object, as if he had made it with Enchantment magic. If used to undo or modify someone else's creation, a Quick contest of skill vs. the creation's Power is rolled. Attempts to modify or undo one's own creation automatically succeed.
The GM may apply modifiers to the skill roll based on a number of factors, ranging from size to complexity.
This skill cannot be learned by a person who has never visited Cerebrospace! Furthermore, it can only be practiced and studied in C-space.