IN MAGNETIC SOURCE IMAGING(MSI), super-sensitive superconducting detectors sample the tiny magnetic fields that come from electrical signals flowing through the body. MSI has some advantages over more established imaging methods such as MRI or PET in that it has a sharper time resolution (it can produce more images per second) and does not base its imaging on local blood flow (which can lag behind the actual activity of interest, in the heart or brain, say). Sam Williamson of NYU (212-998-7692) has previously made detailed maps of the auditory cortex, showing where in the brain tones of different pitch are perceived. At the recent meeting of the American Physical Society in Los Angeles, Williamson reported on the behavior over time of signals received in the various stages of the visual cortex. In particular, he showed that when a subject is given a visual cue, such as the sight of a checkerboard pattern, parts of the visual cortex light up in a succession of stages, for periods as long as 30 seconds, suggesting hints of a "remembering" pathway in the brain. Each part in this pathway seems to have its own memory lifetime. (Science, 3 April 1998.)