The caster implant allows a user to “rent out” some of their brain capacity, to be used for computational processing. By design, the data being processed is not experienced by the user in any way, as it is intended to act as a secure method of processing for those who make use of it. Under exceptional circumstances however, some users may catch glimpses of what their brains have worked through in the aftermath.
Some people make a living by renting out their capacity several hours a day, a group which is commonly referred to as “Cloudheads.” Most companies using cloudheads for cheap processing are certified, but there have been stories of well-paying, uncertified companies, whose work may or may not have resulted in users having horrible visions, or hearing voices outside of their designated processing times. Caster corporations deny any liability for these occurrences, as they are considered malware on a platform that is otherwise perfectly safe, so long as the users only deal with licensed individuals and institutions.