MENTAL ROTATION STUDIED BY FUNCTIONAL MAGNETIC-RESONANCE-IMAGING AT HIGH-FIELD (4 TESLA) - PERFORMANCE AND CORTICAL ACTIVATION

We studied the performance and cortical activation patterns during a m ental rotation task (Shepard & Metzler, 1971) using functional magneti c resonance imaging (MRI) at high field (4 Tesla). Twenty-four human s ubjects were imaged (fMRI group), whereas six additional subjects perf ormed the task without being imaged (control group). All subjects were shown pairs of perspective drawings of 3D objects and asked to judge whether they were the same or mirror images. The measures of performan ce examined included (1) the percentage of errors, (2) the speed of pe rformance, calculated as the inverse of the average response time, and (3) the rate of rotation for those object pairs correctly identified as ''same.'' We found the following: (1) Subjects in the fMRI group pe rformed well outside and inside the magnet, and, in the latter case, b efore and during data acquisition. Moreover, performance over time imp roved in the same manner as in the control group. These findings indic ate that exposure to high magnetic fields does not impair performance in mental rotation. (2) Functional activation data were analyzed from 16 subjects of the fMRI goup. Several cortical areas were activated du ring task performance. The relations between the measures of performan ce above and the magnitude of activation of specific cortical areas we re investigated by anatomically demarcating these areas of interest an d calculating a normalized activation for each one of them. (3) We use d the multivariate technique of hierarchical tree modeling to determin e functional clustering among areas of interest and performance measur es. Two main branches were distinguished: One comprised areas in the r ight hemisphere and the extrastriate and superior parietal lobules bil aterally whereas the other comprised areas of the left hemisphere and the frontal pole bilaterally; all three performance measures above clu stered with the former branch. Specifically, performance outcome (''pe rcentage of errors'') clustered with the parieto-occipital subcluster, whereas both the speed of performance and the rate of mental rotation clustered with the right precentral gyrus. We conclude that the menta l rotation paradigm used involves the cooperative interaction of funct ional groups of cortical areas of which some are probably more specifi cally associated with performance, whereas others may serve a more gen eral function within the task constraints.