The hippocampus binds movements to their temporal position in a motor sequence

A plethora of daily motor tasks consist of sequences of movements or steps that need to be performed in a specific order. Yet, it remains unclear how the brain represents sequential motor actions in a way that preserves their temporal order. Here, we used multivoxel pattern similarity analysis of functional Magnetic Resonance Imaging (fMRI) data acquired during motor sequence practice to investigate whether the hippocampus, a brain region known to support temporal order in the non-motor memory domain, represents information about the temporal order of sequential motor actions. We also examined such representation in other regions of the motor network (i.e., the premotor cortex (PMC), supplementary motor area (SMA), anterior superior parietal lobule (aSPL) and striatum) known for their critical role in motor sequence learning. Our results show that hippocampal activation patterns carried information about movements in their learned temporal position in the sequence, but not about movements or positions in random movement patterns. A similar pattern of results was observed in the striatum. Our data also indicate that multivoxel patterns in M1, SMA and aSPL carried movement-based information while the PMC represented both movement- and position-based information. Altogether, our findings provide novel insight into the role of the hippocampus in the motor memory domain and point to its capacity to bind movements to their temporal position in a motor sequence. Our results also deepen our understanding of how striatal and cortical regions contribute to motor sequence learning via position and movement coding.