(A) Summary diagram of the different roles of dSPNs and iSPNs at each level of the behavioral hierarchy. At the sequence level, both dSPNs and iSPNs signal sequence start/stop. At the subsequence level, the indirect pathway preferentially encodes between-subsequence switch. At the element level, both direct and indirect pathways are involved in action execution with different neuronal dynamics. The magnitude difference between the proportions of dSPNs or iSPNs at each hierarchical level is indicated with greater-than (‘>‘), much greater-than (‘>>‘) and less-than (‘<‘) signs. (B) Striatal direct and indirect pathways dynamically coordinate their activity during sequence execution. The different subpopulations of dSPNs and iSPNs coordinate their activity to support the start/stop of the sequence, the execution of the elemental actions, and the switch between subsequences. The ‘up’ or ‘down’ arrows indicate the positive or negative modulation of firing rate in each neuronal subpopulation, respectively.