Interval and ordinal properties of sequences are associated with distinct premotor areas

Lesion and imaging studies have suggested that the premotor cortex (PMC) is a crucial component in the neural network underlying the processing of seq uential information. However, whether different aspects of sequential infor mation like interval and ordinal properties are supported by different anat omical regions, and whether the representation of sequential information wi thin the PMC is necessarily related to motor requirements, remain open ques tions. Brain activations were investigated during a sequence encoding parad igm in 12 healthy subjects using functional magnetic resonance imaging. Sub jects had to attend either to the interval or to the ordinal information of a sequence of visually presented stimuli and had to encode the relevant in formation either before motor reproduction or before perceptual monitoring. Although interval and ordinal information led to activations within the sa me neural network, direct comparisons revealed significant differences. The pre-supplementary motor area (preSMA), the lateral PMC, the frontal opercu lar cortex as well as basal ganglia and the left lateral cerebellar cortex (CE) were activated significantly more strongly by interval information, wh ereas the SMA, the frontal eye field, the primary motor cortex (MI), the pr imary somatosensory cortex, the cuneus as well as the medial CE and the tha lamus were activated more strongly by ordinal information, In addition, ser ial encoding before reproduction led to higher activations than serial enco ding before monitoring in the preSMA, SMA, MI and medial CE. Our findings s uggest overlapping but different kinds of sequential representation, depend ing on both the ordinal and interval aspects as well as motor requirements.