Cortical areas with enhanced activation during object-centred spatial information processing - A PET study

The phenomenon of object-centred unilateral neglect suggests that some neur al networks process spatial information relative to reference objects. To e xamine object-centred information processing, we measured regional cerebral blood flow in 11 normal subjects with PET. During each PET scan, a subject viewed a sample stimulus followed by a cue on a video screen, The sample c onsisted of two polygons, termed 'objects', each located in a corner of the screen. A small target spot appeared in a corner of each polygon, There we re two tasks: the visuomotor task and the matching-to-sample task, In the v isuomotor task, the subject moved a joystick in a direction indicated by ei ther the location of the target spot inside the object (if object-centred c oordinates were operative) or the location of the object relative to the vi deo screen (if screen-centred coordinates were operative;), In the matching -to-sample task, the subject moved the joystick to report whether the relev ant spatial information (object- or screen-centred) in the cue matched the sample. In both the visuomotor and the matching-to-sample task, use of obje ct-centred (versus screen- or viewer-centred) information caused augmented activation in the inferior occipitotemporal cortex, bilaterally, in the lef t superior occipital gyrus, and in both the thalamus and the brainstem, In addition, in the visuomotor task such activation occurred in the right post erior parietal cortex and in the left ventral premotor, dorsolateral prefro ntal and anterior supplementary motor areas. These findings suggest the inv olvement of the occipitotemporal cortex and a broad frontoparietal network when, as in the visuomotor task, object-centred information guides movement , When the same data underlie declarative reports, as in the matching-to-sa mple task, thp occipitotemporal cortex remains engaged but frontoparietal n etwork diminishes in importance.