Neural substrates for serial reaction time tasks in pigeons.

Most behavior is composed of action sequences. Pigeons were often used as a model to study sequence learning and execution. Yet, virtually nothing is known about the neural structures underlying sequential behavior in pigeons. We therefore applied a serial reaction time task (SRTT) that is commonly used to investigate sequential behavior. During task performance either the nidopallium caudolaterale (NCL) or the nidopallium intermedium medialis pars laterale (NIMl) was transiently inactivated with tetrodotoxin (TTX). Since prefrontal structures play a role in sequence acquisition and performance in mammals and since the NCL is functionally analogous to the prefrontal cortex, NCL was chosen a possibly critical structure of our study. The NIMl is equivalent by hodology and topology to the song nucleus LMAN. Since LMAN plays a key role in song learning and since song consists of learned vocalizatory sequences, we hypothesized that NIMl could also be a candidate for sequence performance in a non-songbird. Moreover, TTX injections into the entopallium were performed as a control. Indeed, inactivation of both the NCL and the NIMl resulted in an increase of sequence specific errors. Hence, we could identify components of neural systems in the pigeon that underlie sequence execution.