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 healthy volu nteers with PET (positron emission tomography). The main purpose was t o map the areas of the human brain that changed rCBF during (1) the st orage, (2) retrieval from long-term memory, and (3) recognition of com plex visual geometrical patterns. A control measurement was done with subjects at rest. Perception and learning of the patterns increased rC BF in V1 and in 17 cortical fields located in the cuneus, the lingual, fusiform, inferior temporal, occipital, and angular gyri, the precune us, and the posterior part of superior parietal lobules. In addition, rCBF increased in the anterior hippocampus, anterior cingulate gyrus, and in several fields in the prefrontal cortex. Recognition of the pat terns increased rCBF in 18 identically located fields overlapping thos e activated in learning. In addition, recognition provoked differentia lly localized increases in the pulvinar, posterior hippocampus, and pr efrontal cortex. Learning and recognition of the patterns thus activat ed identical visual regions, but different extravisual regions. A surp rising finding was that the hippocampus was also active in recognition . Recall of the patterns from long-term memory was associated with rCB F increases in yet different fields in the prefrontal cortex, and the anterior cingulate cortex. In addition, the posterior inferior tempora l lobe, the precuneus, the angular gyrus, and the posterior superior p arietal lobule were activated, but not any spot within the occipital c ortex. Activation of V1 or immediate visual association areas is not a prerequisite for visual imagery for the patterns. The only four field s activated in storage recall and recognition were those in the poster ior inferior temporal robe, the precuneus, the angular gyrus, and the posterior superior parietal lobule. These might be the storage sites f or such visual patterns. If this is true, storage, retrieval, and reco gnition of complex visual patterns are mediated by higher-level visual areas. Thus, visual learning and recognition of the same patterns mak e use of identical visual areas, whereas retrieval of this material fr om the storage sites activates only a subset of the visual areas. The extravisual networks mediating storage, retrieval, and recognition dif fer, indicating that the ways by which the brain accesses the storage sites are different.