Shaping action sequences in basal ganglia circuits

•The basal ganglia are critical for chunking motor elements into action sequences.•Consolidation of motor sequences is paralleled by decreases in neural variability.•Neural activity related to action sequences emerges in basal ganglia circuits.•Sequence-related activity is differentially expressed in basal ganglia subcircuits.•Corticostriatal plasticity is critical for neural and behavioral crystallization.

Many behaviors necessary for organism survival are learned anew and become organized as complex sequences of actions. Recent studies suggest that cortico-basal ganglia circuits are important for chunking isolated movements into precise and robust action sequences that permit the achievement of particular goals. During sequence learning many neurons in the basal ganglia develop sequence-related activity - related to the initiation, execution, and termination of sequences - suggesting that action sequences are processed as action units. Corticostriatal plasticity is critical for the crystallization of action sequences, and for the development of sequence-related neural activity. Furthermore, this sequence-related activity is differentially expressed in direct and indirect basal ganglia pathways. These findings have implications for understanding the symptoms associated with movement and psychiatric disorders.