ROLE OF THE HUMAN ROSTRAL SUPPLEMENTARY MOTOR AREA AND THE BASAL GANGLIA IN MOTOR SEQUENCE CONTROL - INVESTIGATIONS WITH H-2 O-15 PET

The aim of this study was to investigate the functional anatomy of dis tributed cortical and subcortical motor areas in the human brain that participate in the central control of overlearned complex sequential u nimanual finger movements. On the basis of previous research in nonhum an primates, a principal involvement of basal ganglia (medial premotor loops) was predicted for central control of finger sequences performe d automatically. In pertinent areas, a correlation of activation level s with the complexity of a motor sequence was hypothesized. H-2 O-15 p ositron emission tomography (PET) was used in a group of seven healthy male volunteers [mean age 32.0 +/- 10.4 yr] to determine brain region s where levels of regional cerebral blood flow (rCBF) correlated with graded complexity levels of five different key-press sequences. All se quences were overlearned before PET and involved key-presses of finger s II-V of the right hand. Movements of individual fingers were kept co nstant throughout all five conditions by external pacing at 1-Hz inter vals. Positive correlations of rCBF with increasing sequence complexit y were identified in tile contralateral rostral supplementary motor ar ea (pre-SMA) and the associated pallidothalamic loop, as well as in ri ght parietal area 7 and ipsilateral primary motor cortex (M1). In cont rast, while rCBF in contralateral M1 and and extensive parts of caudal SMA was increased compared with rest during task performance, signifi cant correlated increases of rCBF with sequence complexity were not ob served. Inverse correlations of rCBF with increasing sequence complexi ty were identified in mesial prefrontal-, medial temporal-, and anteri or cingulate areas. The findings provide further evidence in humans su pporting the notion of a segregation of SMA into functionally distinct subcomponents: although pre-SMA was differentially activated dependin g on the complexity of a sequence of learned finger movements, such mo dulation was not detectable in caudal SMA (except the most antero-supe rior part), implicating a motor executive role. Our observations of co mplexity-correlate rCBF increases in anterior globus palllidus suggest a specific role for the basal ganglia in the process of sequence faci litation and control. They may act to filter and focus input from moto r cortical areas as patterns of action become increasingly complex.