Nidopallium caudolaterale neuronal responses during serial-order behaviour in pigeons

Serial-order behaviour is the ability to complete a sequence of responses in order to obtain a reward. Serial-order tasks can be thought of as either externally-ordered (EO) such that the order of responses is predetermined, or internally-ordered (IO) such that the subject determines the order of responses from trial to trial. Ordinal knowledge (representation of first, second, or third etc.) is a key component of successful serial-order behaviour, and is considered a higher-order cognitive function. The nidopallium caudolaterale (NCL) is the avian equivalent to the prefrontal cortex, an area of the primate brain important for serial-order behaviour. The importance of the NCL for serial-order behaviour, however, is still unknown. In the current study, we trained pigeons to complete either three-item EO or IO tasks and recorded single-neuron activity from the NCL to determine whether neurons in the NCL code ordinal knowledge. Our results support the view that the NCL is involved in serial-order behaviour by coding ordinal position, at least with respect to the IO task. The absence of any ordinal coding during the EO task could be explained by the different strategies that birds adopt between the EO and IO tasks.