Transient activity in the human calcarine cortex during visual-mental imagery: An event-related fMRI study

Although it is largely accepted that visual-mental imagery and perception d raw on many of the same neural structures, the existence and nature of neur al processing in the primary visual cortex (or area V1) during Visual image ry remains controversial. We tested two general hypotheses: The first Nas c hat V1 is activated only when images with many details are formed and used, and the second was that V1 is activated whenever images are formed, even i f they are not necessarily used to perform a task. We used event-related fu nctional magnetic resonance imaging (ER-fMRI) to detect and characterize th e activity in the calcarine sulcus (which contains the primary visual corte x) during single instances of mental imagery. The results revealed reproduc ible transient activity in this area whenever participants generated or eva luated a mental image. This transient activity was strongly enhanced when p articipants evaluated characteristics of objects; whether or not details ac tually needed to be extracted from the image to perform the task. These res ults show that visual imagery processing commonly involves the earliest sta ges of the visual system.