FUNCTIONAL-ANATOMY OF THE MENTAL REPRESENTATION OF UPPER EXTREMITY MOVEMENTS IN HEALTHY-SUBJECTS

1. Differences in the distribution of relative regional cerebral blood How during motor imagery and execution of a joy-stick movement were i nvestigated in six healthy volunteers with the use of positron emissio n tomography (PET). Both tasks were compared with a common baseline co ndition, motor preparation, and with each other. Data were analyzed fo r individual subjects and for the group, and areas of significant flow differences were related to anatomy by magnetic resonance imaging (MR I). 2. Imagining movements activated a number of frontal and parietal regions: medial and lateral premotor areas, anterior cingulate areas, ventral opercular premotor areas, and parts of superior and inferior p arietal areas were all activated bilaterally when compared with prepar ation to move. 3. Execution of movements compared with imagining movem ents led to additional activations of the left primary sensorimotor co rtex and adjacent areas: dorsal parts of the medial and lateral premot or cortex; adjacent cingulate areas; and rostral parts of the left sup erior parietal cortex. 4. Functionally distinct rostral and caudal par ts of the posterior supplementary motor area (operationally defined as the SMA behind the coronal plane at the level of the anterior commiss ure) were identified. In the group, the rostral part of posterior SMA was activated by imagining movements, and a more caudoventral part was additionally activated during their execution. A similar dissociation was observed in the cingulate areas. Individual subjects showed that the precise site of these activations varied with the individual anato my; however, a constant pattern of preferential activation within sepa rate but adjacent gyri of the left hemisphere was preserved. 5. Functi onally distinct regions were also observed in the parietal lobe: the c audal part of the superior parietal cortex [medial Brodmann area (BA) 7] was activated by imagining movements compared with preparing to exe cute them, whereas the more rostral parts of the superior parietal lob e (BA 5), mainly on the left, were additionally activated by execution of the movements. 6. Within the operculum, three functionally distinc t areas were observed: rostrally, prefrontal areas (BA 44 and 45) were more active during imagined than executed movements; a ventral premot or area (BA 6) was activated during both imagined and executed movemen ts; and more caudally in the parietal lobe. an area was found that was mainly activated by execution, presumably SII. 7. These data suggest that imagined movements can be viewed as a special form of ''motor beh avior'' that, when compared with preparing to move, activate areas ass ociated heretofore with selection of actions and multisensory integrat ion. The neural substrate of imagining a movement differs from that in volved in its execution most notably by the absence of activation of t he primary sensorimotor cortex in the central sulcus and immediately a djacent premotor, cingulate, and parietal structures.