A brain atlas of the carrion crow (Corvus corone)

Abstract

Corvidae, passerine songbirds such as jays, crows, and ravens known as corvids, have become model systems for the study of avian cognition. The superior cognitive capabilities of corvids mainly emerge from a disproportionally large telencephalon found in these species. However, a systematic mapping of the neuroanatomy of the corvid brain, and the telencephalon in particular, is lacking so far. Here, we present a brain atlas of the carrion crow, Corvus corone, with special emphasis on the telencephalic pallium. We applied four staining techniques to brain slices (Nissl, myelin, combination of Nissl and myelin, and tyrosine hydroxylase targeting catecholaminergic neurons). This allowed us to identify brain nuclei throughout the brain and delineate the known pallial subdivisions termed hyperpallium, entopallium, mesopallium, nidopallium, arcopallium, and hippocampal complex. The extent of these subdivisions and brain nuclei are described according to stereotaxic coordinates. In addition, 3D depictions of pallial regions were reconstructed from these slices. While the overall organization of the carrion crow's brain matches other songbird brains, the relative proportions and expansions of associative pallial areas differ considerably in agreement with enhanced cognitive skills found in corvids. The presented global organization of the crow brain in stereotaxic coordinates will help to guide future neurobiological studies in corvids.

Input and Output Connections of the Crow Nidopallium Caudolaterale

“…A simple beak biting rod was added so that the beak would be held in a 45° angle below the horizontal axis. Based on previously described coordinates ( Kersten et al, 2022 ), NCLd was accessed through a small craniotomy centered at 3.5 mm posterior and 11.5 mm lateral relative to the center of the bifurcation of the superior sagittal sinus. This AP position corresponds to “AP 4.6” in our previously published carrion crow brain atlas ( Kersten et al, 2022 ).…”

“…The extent of the NCL is typically estimated based on an immunohistochemical staining method against tyrosine hydroxylase (TH), the rate-limiting enzyme in the production of dopamine ( Divac and Mogensen, 1985 ; Kröner and Güntürkün, 1999 ). These midbrain, dopaminergic afferents are denser within the NCL compared with neighboring nidopallial areas, which signifies another similarity to the PFC ( Divac and Mogensen, 1985 ; von Eugen et al, 2020 ; Kersten et al, 2022 ). Notably, the anti-TH method identifies a single portion of the pigeon caudal nidopallium, whereas it distinguishes three caudal nidopallial areas in the carrion crow and other songbirds (i.e., a dorsal, medial, and ventral NCL; von Eugen et al, 2020 ; Kersten et al, 2022 ).…”

“…These midbrain, dopaminergic afferents are denser within the NCL compared with neighboring nidopallial areas, which signifies another similarity to the PFC ( Divac and Mogensen, 1985 ; von Eugen et al, 2020 ; Kersten et al, 2022 ). Notably, the anti-TH method identifies a single portion of the pigeon caudal nidopallium, whereas it distinguishes three caudal nidopallial areas in the carrion crow and other songbirds (i.e., a dorsal, medial, and ventral NCL; von Eugen et al, 2020 ; Kersten et al, 2022 ). Given its position relative to the readily identifiable dorsal arcopallial tract (DA), the projections of the crow's dorsal NCL (NCLd) to the arcopallium appear to correspond to the arcopallial projections of the NCL in pigeons ( von Eugen et al, 2020 ; Kersten et al, 2022 ).…”

“…Notably, the anti-TH method identifies a single portion of the pigeon caudal nidopallium, whereas it distinguishes three caudal nidopallial areas in the carrion crow and other songbirds (i.e., a dorsal, medial, and ventral NCL; von Eugen et al, 2020 ; Kersten et al, 2022 ). Given its position relative to the readily identifiable dorsal arcopallial tract (DA), the projections of the crow's dorsal NCL (NCLd) to the arcopallium appear to correspond to the arcopallial projections of the NCL in pigeons ( von Eugen et al, 2020 ; Kersten et al, 2022 ). Therefore, comparative functional studies were focused on investigating the crow's NCLd over the past decade ( Veit and Nieder, 2013 ; Kersten et al, 2022 ; Wagener and Nieder, 2023 ).…”

“…Given its position relative to the readily identifiable dorsal arcopallial tract (DA), the projections of the crow's dorsal NCL (NCLd) to the arcopallium appear to correspond to the arcopallial projections of the NCL in pigeons ( von Eugen et al, 2020 ; Kersten et al, 2022 ). Therefore, comparative functional studies were focused on investigating the crow's NCLd over the past decade ( Veit and Nieder, 2013 ; Kersten et al, 2022 ; Wagener and Nieder, 2023 ). However, the brain-wide connectivity of the NCLd in the crow, or any other songbird, has not yet been explored systematically ( Wild and Farabaugh, 1996 ; Paterson and Bottjer, 2017 ).…”