Visual Memory, Visual Imagery, and Visual Recognition of Large Field Patterns by the Human Brain: Functional Anatomy by Positron Emission Tomography

We measured the regional cerebral blood flow (rCBF) in 11 healthyvolunteers with PET (positron emission tomography). The mainpurpose was to map the areas of the human brain that changedrCBF during (1) the storage, (2) retrieval from long-term memory,and (3) recognition of complex visual geometrical patterns.A control measurement was done with subjects at rest. Perceptionand learning of the patterns increased rCBF in V1 and in 17cortical fields located in the cuneus, the lingual, fusiform,inferior temporal, occipital, and angular gyri, the precuneus,and the posterior part of superior parietal lobules. In addition,rCBF increased in the anterior hippocampus, anterior cingulategyrus, and in several fields in the prefrontal cortex. Recognitionof the patterns increased rCBF in 18 identically located fieldsoverlapping those activated in learning. In addition, recognitionprovoked differentially localized increases in the pulvinar,posterior hippocampus, and prefrontal cortex. Learning and recognitionof the patterns thus activated identical visual regions, butdifferent extravisual regions. A surprising finding was thatthe hippocampus was also active in recognition. Recall of thepatterns from long-term memory was associated with rCBF increasesin yet difierent fields in the prefrontal cortex, and the anteriorcingulate cortex. In addition, the posterior inferior temporallobe, the precuneus, the angular gyrus, and the posterior superiorparietal lobule were activated, but not any spot within theoccipital cortex. Activation of V1 or immediate visual associationareas is not a prerequisite for visual imagery for the patterns.The only four fields activated in storage recall and recognitionwere those in the posterior inferior temporal lobe, the precuneus,the angular gyrus, and the posterior superior parietal lobule.These might be the storage sites for such visual patterns. Ifthis is true, storage, retrieval, and recognition of complexvisual patterns are mediated by higher-level visual areas. Thus,visual learning and recognition of the same patterns make useof identical visual areas, whereas retrieval of this materialfrom the storage sites activates only a subset of the visualareas. The extravisual networks mediating storage, retrieval,and recognition differ, indicating that the ways by which thebrain accesses the storage sites are different.