The synthesis of complex, coordinated movements from simple actions is an i
mportant aspect of motor control. Lesion studies have revealed specific bra
in areas, particularly the cerebellum, to be essential for a variety of coo
rdinated movements, and lend support to the view that the cerebellum is eng
aged in the integration of simple movements into compound ones. A PET study
was therefore conducted to show which brain areas were active specifically
during the coordinated execution of an arm and finger movement to visual t
argets. A two-by-two factorial design was employed, in which subjects eithe
r made arm or finger movements alone, made coordinated arm-finger movements
, or made no movements. Voxels were identified where activity was significa
ntly greater during the execution of coordinated movements than when moveme
nts were made alone and in which this increased activity could not be accou
nted for simply by the additive effects of the activations for each movemen
t in isolation. The behavioral results showed that subjects coordinated arm
and finger movements well during coordination scans. Coordination-specific
activations were found in left anterior lobe and bilaterally in the parame
dian lobules of the cerebellum. These are known to receive forelimb-specifi
c spinocerebellar proprioceptive inputs that may be related to multijoint m
ovements. The same areas also receive corticocerebellar afference from moto
r areas that may convey efference copy information to the cerebellum. Coord
ination-specific activations were also seen in areas of the posterior parie
tal cortex. The results provide direct evidence in healthy human subjects o
f specific cerebellar engagement during the coordination of movement, over
and above the control of constituent movements. (C) 2001 Academic Press.