The avian brain is the central organ of the nervous system in birds. Birds possess large, complex brains, which process, integrate, and coordinate information received from the environment and make decisions on how to respond with the rest of the body. Like in all chordates, the avian brain is contained within the skull bones of the head.
The bird brain is divided into a number of sections, each with a different function. The cerebrum or telencephalon is divided into two hemispheres, and controls higher functions. The telencephalon is dominated by a large pallium, which corresponds to the mammalian cerebral cortex and is responsible for the cognitive functions of birds. The pallium is made up of several major structures: the hyperpallium, a dorsal bulge of the pallium found only in birds, as well as the nidopallium, mesopallium, and archipallium. The bird telencephalon nuclear structure, wherein neurons are distributed in three-dimensionally arranged clusters, with no large-scale separation of white matter and grey matter, though there exist layer-like and column-like connections. Structures in the pallium are associated with perception, learning, and cognition. Beneath the pallium are the two components of the subpallium, the striatum and pallidum. The subpallium connects different parts of the telencephalon and plays major roles in a number of critical behaviours. To the rear of the telencephalon are the thalamus, midbrain, and cerebellum. The hindbrain connects the rest of the brain to the spinal cord.
The size and structure of the avian brain enables prominent behaviours of birds such as flight and vocalization. Dedicated structures and pathways integrate the auditory and visual senses, strong in most species of birds, as well as the typically weaker olfactory and tactile senses. Social behaviour, widespread among birds, depends on the organisation and functions of the brain. Some birds exhibit strong abilities of cognition, enabled by the unique structure and physiology of the avian brain.
Structure and function
Telencephalon
The telencephalon, or forebrain, is generally a large structure in birds. It is made up of three primary domains: the striatal domain, the pallidal domain, and the pallial domain.
Pallium
The pallial domain is divided into two main parts: the Wulst, or hyperpallium, at the dorsal surface of the pallium, and the dorso-ventricular ridge, which comprises the nidopallium, arcopallium, and archipallium. The circuitry of the avian brain is organised such that circuits for processes such as vision and cognition pass between the structures of the pallium, with connections both horizontally and vertically oriented within the pallium. In the sensory areas of the pallium, neurons display a layer-like organisation into columns, with horizontal connections; hence, the part of the pallium responsible for sensory circuitry is also called the sensory cortex in birds.
Within the pallium, the nidopallium caudolaterale is thought to be a centre of goal-directed action. It is the part of the pallium that has the most innervation sensitive to dopamine, and has a structure suggesting strong dopamine control. Neural activity in the nidopallium caudolaterale is correlated with rewards, rules, categories, and information held in the memory. The nidopallium caudolaterale is also proportionally much larger in birds with stronger cognitive abilities. Showing diversity in bird brains and potentially the role of the nidopallium caudolaterale is that structure's separation into multiple structures in songbirds.
Lateralisation
The avian telencephalon, like its human counterpart, is organised into two distinct hemispheres. Functions such as song learning in songbirds, vision, auditory, and olfactory, and magnetic sensory systems are all lateralised, meaning that one hemisphere of the brain dominates a certain function. The left hemisphere of the brain dominates activities that demand the separation of important stimuli from distracting ones, while the right hemisphere is more easily distracted and has a broad attention. The right hemisphere also dominates fear and escape responses. In zebra finches (Taeniopygia guttata), the left hemisphere also is dominant in learning tasks. Birds can sense the orientation of magnetic fields, and use them to help navigate. The right hemisphere of the brain is dominant in the magnetic sense.