Given its strategic location, it is ironic that the primary visual cortex is not even necessary for all forms of visual perception. Brain imaging in dreaming volunteers (no easy feat, given the tight quarters and the noisy banging inside a scanner) suggests that activity in the primary visual cortex is curtailed in the rapid eye movement (REM) phase of sleep, when most dreams occur, compared with non-REM sleep, when little dreaming takes place. Furthermore, patients with damage to their primary visual cortex dream without any concomitant loss of visual content.
