FLICKER POTENTIALS AND THE ALPHA RHYTHM IN MAN

Abstract

Flicker potentials in response to intermittent light stimulation were observed in the electroencephalograms of 21 normal adult <$ subjects. Subjects having a low % time a rhythm showed the widest frequency range of flicker following. In amplitude and regularity flicker potentials were best at about the frequency of the a rhythm. They were confined to the occipital region except for occasional appearance at the vertex. They required a period of time for organization at the beginning of a train of flashes. Once organized, they showed an inherent rhythmicity and could continue for a short time after the cessation of the stimulus. "On" responses to isolated light flashes were observed in some subjects, but "off" responses were never seen and were considered absent even in the phenomenon of "doubling" or apparent flicker following at double the flash frequency. Flicker-following was interpreted as a succession of over-lapping "on" responses comparable to the slowest components of the cortical response to optic nerve stimulation studied by Bishop and collaborators in the cat and rabbit. The cortical elements involved included not only some of those whose spontaneous activity might be recorded as the [alpha] rhythm but also others of different natural frequency which were ordinarily prevented from synchronization by the dominant a rhythm.