Brain connectivity underlying cognition without a neocortex – EVONECTOME

Tool use behaviors have evolved not only in primates but also in some birds (e.g. parrots and crows) and even in some teleost fish (e.g. wrasses and cichlids). As birds and teleosts do not have a six-layered neocortex, these similar cognitive functions must have evolved independently in the lineages of mammals, birds, and teleosts (convergent evolution). Our research project aims to identify the necessary conditions for the emergence of such cognitive abilities during vertebrate evolution.

The ability for problem solving and sequential object manipulation is the prerequisite condition for evolving tool use ability. The EVONECTOME project investigates the connectivity (TASK 1) and functions (TASKs 2-4) of associative brain areas involved in a problem solving task and sequential object manipulation in parrots and cichlids. We propose to use Pyrrhura molinae as a parrot model and Amatitlania nigrofasciata as a cichlid model, which are optimal for combining anatomical and behavioral examinations.

TASK 1: We will take a connectomic approach using ex-vivo diffusion MRI to visualize neuronal networks with regard to putative associative areas in the pallium. The main goal is to reveal the connectivity of the associative areas, notably with premotor/motor areas. The results will verify whether there is a shared network logic for cognitive-motor integration in primates, parrots, and cichlids.

TASK 2: To examine problem solving and object manipulation abilities of parrots and cichlids, we will perform two different behavioral tasks: a puzzle box task and operant conditioning tasks that require object manipulation as responses. After the behavioral tests, the brain areas involved in these behaviors will be examined in TASK 3 and TASK 4.

TASK 3: Neuronal activation during the behavioral tasks will be visualized by functional MRI, using Manganese-enhanced MRI (MEMRI). By detecting large-scale brain activity during the behavioral tasks (TASK 2), we expect to identify brain areas involved in problem solving and object manipulation.

TASK 4: To assess the role of dopamine (DA) neurotransmission in the behavioral tests, we will destruct DA fibers in the associative areas by a local injection of 6-hydroxydopamine (6-OHDA). DA is known to play a critical role in various higher-order cognitive functions in mammals. If DAergic disruption in non-homologous brain areas leads to the same behavioral effects in mammals, birds, and teleosts, this will further support the importance of DA in the convergent evolution of higher-order cognitive functions.

Altogether, our study will give an insight into how morphologically diversified nervous systems achieved similar cognitive functions during evolution. If the same network pattern emerged independently in primates, parrots, and cichlids, this would indicate the existence of a limited degree of biological freedom (high constraints) for the evolution of intelligence in vertebrate brains.