Identification of two forebrain structures that mediate execution of memorized sequences in the pigeon.

The execution of action sequences is the basis of most behavior. However, little is known about the neural foundation of visuomotor sequence execution in birds, although pigeons are a classic model animal to study sequence learning and production. Recently, we identified two structures in the pigeon brain, the nidopallium intermedium medialis pars laterale (NIML) and the nidopallium caudolaterale (NCL), that are involved in the execution of a serial reaction time task (SRTT). In the SRTT sequence execution is always cue guided. Thus the previous study could not unambiguously clarify whether NCL and NIML contribute to a memory-based execution of sequential behavior. In addition, a possibly differential role of these two structures could not be identified. Therefore, the present study was conducted to further elucidate the role of NCL and NIML in sequence execution in a task where pigeons performed a memorized four-item sequence. Transient inactivation of each NIML and NCL severely impaired sequence execution. The results confirm and extend our previous findings. NIML and NCL seem to store sequence information in parallel. However, the results support the hypothesis that NCL, in contrast to NIML, is especially required for sequence initiation.