Nidopallium

The nidopallium, meaning nested pallium, is the region of the avian brain that is used mostly for some types of executive functions but also for other higher cognitive tasks. The region was renamed nidopallium in 2002 during the Avian Brain Nomenclature Consortium because the prior name, neostriatum, suggested that the region was used for more primitive functions as the neostriatum in mammalian brains is sub-cortical.

The avian nidopallium is an area of the cortical telencephalon of the avian forebrain, and is itself subdivided into smaller regions as a result of further functional localisation. It has been apportioned along the rostrocaudal (anteroposterior) axis into three hypothetical segments: the rostral, intermediate and caudal nidopallium. These three regions are themselves trichotomised: the caudal nidopallium, for example, aggregates the nidopallium caudocentral (NCC), caudomedial (NCM) and caudolateral (NCL). It is the nidopallium caudolateral which is thought to undertake many of the complex, higher order cognitive functions in birds. Rehkamper et al. (1985) further demarcated the nidopallium into 16 separate sections (distinguished by differing cell densities in these areas), although the previously stated anatomical divisions are generally accepted for most purposes for delineating between the nidopallium's various functional specialisations.

The entire nidopallium region is a compelling area for neuroscientific research, especially in relation to its capacity for complex cognitive function. More specifically, the nidopallium caudolateral appears particularly involved with the aspect of executive function in the avian brain. One study has been performed to demonstrate that this area is in fact largely analogous to the mammalian prefrontal cortex - the region of the brain covering the most rostral section of the frontal lobe, responsible for more complex cognitive behaviour in mammals, such as ourselves. The experiment sought to measure the densities of various neurotransmitter receptors in both the avian NCL and the human prefrontal cortex, using quantitative in-vitro receptor autoradiography. It was found that the NCL contained lower absolute quantities of these neuronal receptors. However, the experiment also revealed that the relative densities of these receptors in both organisms were surprisingly similar. With this, there is the possible implication that the capability for such sophisticated mental processes in these structures is reliant on the receptor architecture of the neurons which comprise them. So despite the nidopallium and prefrontal cortex having evolved separately (an educated assumption), both have achieved similar functions of higher order thought processes via convergent evolution, as a result of influences at the molecular level.

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