COMPLEXITY AFFECTS REGIONAL CEREBRAL BLOOD-FLOW CHANGE DURING SEQUENTIAL FINGER MOVEMENTS

Brain regions activated with complex sequential finger movements were localized by measuring regional cerebral blood flow (rCBF) with positr on emission tomography. Whereas the total number and frequency of fing er movements were kept constant, the complexity of auditory cued seque ntial finger movements of the right hand varied, with sequence length as the independent variable. In four conditions of differing complexit y, the bilateral primary sensorimotor area, left ventral premotor cort ex, posterior supplementary motor area, right superior part of the cer ebellum, and left putamen were consistently and equally activated. Thi s finding suggests an executive role in running sequences, regardless of their length. The right dorsal premotor cortex (Brodmann area 6) an d the right precuneus (Brodmann area 7) showed a linear increase of rc BF as sequence complexity increased. This finding is consistent with t he hypothesis that these areas function in the storage of motor sequen ces in spatial working memory and the production of ongoing sequential movement with reference to that of buffered memory. A similar increas e in the cerebellar vermis and the left thalamus likewise suggests a r ole of these subcortical structures in complexity of sequential finger movements. Conversely, the left inferior parietal lobule showed a dec rease of rCBF as complexity increased. Because short-term phonological storage is localized to this area, we suggest that the visuospatial w orking memory system may suppress other systems not in use. Our findin gs suggest that complex sequential finger movements recruit a discrete set of brain areas, in addition to areas underlying the execution of simple movement sequences.