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 sequential information. However, whether different aspects of sequential information like interval and ordinal properties are supported by different anatomical regions, and whether the representation of sequential information within the PMC is necessarily related to motor requirements, remain open questions. Brain activations were investigated during a sequence encoding paradigm in 12 healthy subjects using functional magnetic resonance imaging. Subjects 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 information either before motor reproduction or before perceptual monitoring. Although interval and ordinal information led to activations within the same neural network, direct comparisons revealed significant differences. The pre-supplementary motor area (preSMA), the lateral PMC, the frontal opercular cortex as well as basal ganglia and the left lateral cerebellar cortex (CE) were activated significantly more strongly by interval information, whereas the SMA, the frontal eye field, the primary motor cortex (MI), the primary somatosensory cortex, the cuneus as well as the medial CE and the thalamus were activated more strongly by ordinal information. In addition, serial encoding before reproduction led to higher activations than serial encoding before monitoring in the preSMA, SMA, MI and medial CE. Our findings suggest overlapping but different kinds of sequential representation, depending on both the ordinal and interval aspects as well as motor requirements.