[Aside] Yesterday I was in at a medico-scientific establishment for what is referred to as an evoked potential test, which basically hooks a bunch of wires to you to test optic, auditory and sensorimotor nerve conductivity. Given my theoretical readings of late — Kittler, Massumi, Virilio — I was naturally as interested in the process as I was in the outcome. Watching the diagnostic screen during one of the tests I couldn't help but notice how noisy one set of results looked. The technician replied that one of the biggest problems during these tests is trying to remove "muscular artefacts" from the results. In other words, muscular activity runs counter to the visioning of the nervous system. I found that poignant for some reason.
The other notable thing that stuck out for me concerned the location of those spots on my scalp that would have electrodes attached to them. Once found, they were marked with a bright red grease pencil. The other use for grease pencils that immediately comes to mind is in marking celluloid film before splicing — before editing went digital, that is. A grease pencil marks the location of film cuts, which are then recombined to form a moving picture; in the evoked potential, meanwhile, a grease pencil marks the location of electrical current cuts, which are then redirected through a diagnostic apparatus to form a moving picture of my nervous system.