Hippocampal formation is required for geometric navigation in pigeons

Amphibian spatial cognition, medial pallium and other supporting telencephalic structures

Vertebrate hippocampal formation is central to conversations on the comparative analysis of spatial cognition, especially in light of variation found in different vertebrate classes. Assuming the medial pallium (MP) of extant amphibians resembles the hippocampal formation (HF) of ancestral stem tetrapods, we propose that the HF of modern amniotes began with a MP characterized by a relatively undifferentiated cytoarchitecture, more direct thalamic/olfactory sensory inputs, and a more generalized role in associative learning-memory processes. As such, hippocampal evolution in amniotes, especially mammals, can be seen as progressing toward a cytoarchitecture with well-defined subdivisions, regional connectivity, and a functional specialization supporting map-like representations of space. We then summarize a growing literature on amphibian spatial cognition and its underlying brain organization. Emphasizing the MP/HF, we highlight that further research into amphibian spatial cognition would provide novel insight into the role of the HF in spatial memory processes, and their supporting neural mechanisms. A more complete reconstruction of hippocampal evolution would benefit from additional research on non-mammalian vertebrates, with amphibians being of particular interest.

A bird's eye view of the hippocampus beyond space: Behavioral, neuroanatomical, and neuroendocrine perspectives

Although the hippocampus is one of the most-studied brain regions in mammals, research on the avian hippocampus has been more limited in scope. It is generally agreed that the hippocampus is an ancient feature of the amniote brain, and therefore homologous between the two lineages. Because birds and mammals are evolutionarily not very closely related, any shared anatomy is likely to be crucial for shared functions of their hippocampi. These functions, in turn, are likely to be essential if they have been conserved for over 300 million years. Therefore, research on the avian hippocampus can help us understand how this brain region evolved and how it has changed over evolutionary time. Further, there is a strong research foundation in birds on hippocampal-supported behaviors such as spatial navigation, food caching, and brood parasitism that scientists can build upon to better understand how hippocampal anatomy, network circuitry, endocrinology, and physiology can help control these behaviors. In this review, we summarize our current understanding of the avian hippocampus in spatial cognition as well as in regulating anxiety, approach-avoidance behavior, and stress responses. Although there are still some questions about the exact number of subdivisions in the avian hippocampus and how that might vary in different avian families, there is intriguing evidence that the avian hippocampus might have complementary functional profiles along the rostral-caudal axis similar to the dorsal-ventral axis of the rodent hippocampus, where the rostral/dorsal hippocampus is more involved in cognitive processes like spatial learning and the caudal/ventral hippocampus regulates emotional states, anxiety, and the stress response. Future research should focus on elucidating the cellular and molecular mechanisms - including endocrinological - in the avian hippocampus that underlie behaviors such as spatial navigation, spatial memory, and anxiety-related behaviors, and in so doing, resolve outstanding questions about avian hippocampal function and organization.

Orientation by environmental geometry and feature cues in the green and black poison frog (Dendrobates auratus)

The ability to use environmental geometry when orienting in space reflects an animal's ability to use a global, allocentric framework. Therefore, understanding when and how animal's use geometry relative to other types of cues in the environment has interested comparative cognition researchers for decades. Yet, only two amphibians have been tested to date. We trained the poison frog Dendrobates auratus to find goal shelters in a rectangular arena, in the presence and absence of a feature cue, and assessed the relative influence of the two types of cues using probe trials. We chose D. auratus because the species has complex interactions with their physical and social environments, including parental care that requires navigating to and from distant locations. We found that, like many vertebrates, D. auratus are capable of using geometric information to relocate goals. In addition, the frogs preferentially used the more reliable feature cue when the location of the feature conflicted with the geometry of the arena. The frogs were equally successful at using the feature cue when it was proximal or distal to the goal shelter, consistent with prior studies that found that D. auratus can use distal cues in a flexible manner. Our results provide further evidence that amphibians can use environmental geometry during orientation. Future studies that examine when and how amphibians use geometry relative to other types of cues will contribute to a more complete picture of spatial cognition in this important, yet understudied, group.

Lateral and medial telencephalic pallium lesions impair spatial memory in goldfish

Fish, like many other animals, navigate to ensure survival. While the telencephalon region of the teleost fish brain is believed to play a critical role in navigation, lesion and electrophysiology studies differ as to whether navigation is situated in the lateral pallium or the medial pallium. To address this inconsistency, we replicated combined behavioral and lesion studies in the goldfish. Goldfish were trained in two navigation tasks testing allocentric navigation on a horizontal plus-maze and a horizontal breadboard to get a reward. The fish were divided randomly into lateral pallium lesion, medial pallium lesion, and sham groups and retested for their success rates. The lateral lesion group had a significant decrease of success on the breadboard task but not on the plus-maze task, whereas the medial lesion affected both tasks significantly. These results suggest that both the medial and lateral pallium are essential for the coding of spatial memory and challenge the assumption that one distinct region of the pallium is involved in spatial memory in teleost.

Navigational roots of spatial and temporal memory structure

Our minds are constantly in transit, from the present to the past to the future, across places we have and have not directly experienced. Nevertheless, memories of our mental time travel are not organized continuously and are adaptively chunked into contexts and episodes. In this paper, I will review evidence that suggests that spatial boundary representations play a critical role in providing structure to both our spatial and temporal memories. I will illustrate the intimate connection between hippocampal spatial mapping and temporal sequencing of episodic memory to propose that high-level cognitive processes like mental time travel and conceptual mapping are rooted in basic navigational mechanisms that we humans and nonhuman animals share. Our neuroscientific understanding of hippocampal function across species may provide new insight into the origins of even the most uniquely human cognitive abilities.

Acute-stress induces the structural plasticity in hippocampal neurons of 15 and 30-day-old chick, Gallus gallus domesticus

To study the stress effect on neuronal architecture in the avian hippocampus (a vital component of the neural circuitry mediating stress responses), chick constitutes an interesting animal model. The hippocampus due to its susceptible and vulnerable nature towards acute-stress effect shows pronounced structural and morphological plasticity. Therefore, to perform a detailed investigation of the acute-stress effect on neuronal architecture in the hippocampus, the present study targets to examine the role of a single acute-stress session of 24-hours food and water deprivation in inducing structural plasticity in 15 and 30-day-old chick by using Golgi-Cox staining technique.The findings of the present study have displayed that the chick hippocampus contains highly spinous multipolar, pyramidal, and stellate neuronal cells, along with four variably shaped spines namely filopodia, thin, stubby, and mushroom, over their dendritic branches. In the hippocampus of a 15-day-old chick, the multipolar projection and the stellate neurons show a significant decrease in their spine density under acute-stress, while the pyramidal projection neurons show a significant increase. All the hippocampus neuronal cells of 30-day-old chicks have shown a significant decrease in their dendritic spine density under stressful environment. Therefore, the present research study establishes structural plasticity in hippocampus neurons due to changes in environmental conditions that may affect the animal's behavior.

Spatial cognition and the avian hippocampus: Research in domestic chicks

In this review, we discuss the functional equivalence of the avian and mammalian hippocampus, based mostly on our own research in domestic chicks, which provide an important developmental model (most research on spatial cognition in other birds relies on adult animals). In birds, like in mammals, the hippocampus plays a central role in processing spatial information. However, the structure of this homolog area shows remarkable differences between birds and mammals. To understand the evolutionary origin of the neural mechanisms for spatial navigation, it is important to test how far theories developed for the mammalian hippocampus can also be applied to the avian hippocampal formation. To address this issue, we present a brief overview of studies carried out in domestic chicks, investigating the direct involvement of chicks' hippocampus homolog in spatial navigation.

Morphology, biochemistry and connectivity of Cluster N and the hippocampal formation in a migratory bird

The exceptional navigational capabilities of migrating birds are based on the perception and integration of a variety of natural orientation cues. The “Wulst” in the forebrain of night-migratory songbirds contains a brain area named “Cluster N”, which is involved in processing directional navigational information derived from the Earth´s magnetic field. Cluster N is medially joined by the hippocampal formation, known to retrieve and utilise navigational information. To investigate the connectivity and neurochemical characteristics of Cluster N and the hippocampal formation of migratory birds, we performed morphological and histochemical analyses based on the expression of calbindin, calretinin, parvalbumin, glutamate receptor type 1 and early growth response protein-1 in the night-migratory Garden warbler (Sylvia borin) and mapped their mutual connections using neuronal tract tracing. The resulting expression patterns revealed regionally restricted neurochemical features, which mapped well onto the hippocampal and hyperpallial substructures known from other avian species. Magnetic field-induced neuronal activation covered caudal parts of the hyperpallium and the medially adjacent hippocampal dorsomedial/dorsolateral subdivisions. Neuronal tract tracings revealed connections between Cluster N and the hippocampal formation with the vast majority originating from the densocellular hyperpallium, either directly or indirectly via the area corticoidea dorsolateralis. Our data indicate that the densocellular hyperpallium could represent a central relay for the transmission of magnetic compass information to the hippocampal formation where it might be integrated with other navigational cues in night-migratory songbirds.

The medial pallium and the spatial encoding of geometric and visual cues in the terrestrial toad, Rhinella arenarum

The medial pallium (MP) of amphibians is the homologue of the mammalian hippocampus, and previous research has implicated MP for locating a using the boundary geometry of an environment. MP-lesioned, sham-operated and intact control terrestrial toads, Rhinella arenarum, were trained to locate a goal in a rectangular arena with a visual feature cue placed on one of the short walls. Whereas the sham-operated and intact subjects successfully learned to locate the goal, the MP-lesioned toads showed no evidence of learning. The data support the hypothesis that the amphibian MP is involved when the boundary geometry of an environment is used to locate a goal, which is consistent with evidence from other vertebrate groups. Curious, however, is that the MP lesions also resulted in the toads' inability to locate the goal based on the visual feature cue. This result supports previous research and suggests that, in contrast to the hippocampal homologue of amniotes, the amphibian medial pallium plays a broader role in spatial learning processes.

The Geometric World of Fishes: A Synthesis on Spatial Reorientation in Teleosts

Fishes navigate through underwater environments with remarkable spatial precision and memory. Freshwater and seawater species make use of several orientation strategies for adaptative behavior that is on par with terrestrial organisms, and research on cognitive mapping and landmark use in fish have shown that relational and associative spatial learning guide goal-directed navigation not only in terrestrial but also in aquatic habitats. In the past thirty years, researchers explored spatial cognition in fishes in relation to the use of environmental geometry, perhaps because of the scientific value to compare them with land-dwelling animals. Geometric navigation involves the encoding of macrostructural characteristics of space, which are based on the Euclidean concepts of "points", "surfaces", and "boundaries". The current review aims to inspect the extant literature on navigation by geometry in fishes, emphasizing both the recruitment of visual/extra-visual strategies and the nature of the behavioral task on orientation performance.

Space, feature, and risk sensitivity in homing pigeons (Columba livia): Broadening the conversation on the role of the avian hippocampus in memory

David Sherry has been a pioneer in investigating the avian hippocampal formation (HF) and spatial memory. Following on his work and observations that HF is sensitive to the occurrence of reward (food), we were interested in carrying out an exploratory study to investigate possible HF involvement in the representation goal value and risk. Control sham-lesioned and hippocampal-lesioned pigeons were trained in an open field to locate one food bowl containing a constant two food pellets on all trials, and two variable bowls with one containing five pellets on 75% (High Variable) and another on 25% (Low Variable) of their respective trials (High-Variable and Low-Variable bowls were never presented together). One pairing of pigeons learned bowl locations (space); another bowl colors (feature). Trained to color, hippocampal-lesioned pigeons performed as rational agents in their bowl choices and were indistinguishable from the control pigeons, a result consistent with HF regarded as unimportant for non-spatial memory. By contrast, when trained to location, hippocampal-lesioned pigeons differed from the control pigeons. They made more first-choice errors to bowls that never contained food, consistent with a role of HF in spatial memory. Intriguingly, the hippocampal-lesioned pigeons also made fewer first choices to both variable bowls, suggesting that hippocampal lesions resulted in the pigeons becoming more risk averse. Acknowledging that the results are preliminary and further research is needed, the data nonetheless support the general hypothesis that HF-dependent memory representations of space capture properties of reward value and risk, properties that contribute to decision making when confronted with a choice.

Importance of the hippocampus for the learning of route fidelity in homing pigeons

The avian hippocampal formation (HF) is thought to regulate map-like memory representations of visual landmarks/landscape features and has more recently been suggested to be similarly important for the perceptual integration of landmarks/landscapes. Aspects of spatial memory and perception likely combine to support the now well-documented ability of homing pigeons to learn to retrace the same route when homing from familiar locations, leading to the prediction that damage to the HF would result in a diminished ability to repeatedly fly a similar route home. HF-lesioned homing pigeons were repeatedly released from three sites to assess the importance of the hippocampus as pigeons gradually learn a familiar route home guided by familiar landmark and landscape features. As expected, control pigeons displayed increasing fidelity to a familiar route home, and by inference, successful perceptual and memory processing of familiar landmarks/landscape features. By contrast, the impoverished route fidelity of the HF-lesioned pigeons indicated an impaired sensitivity to the same landmark/landscape features.

The Mating Call of the Terrestrial Toad, Rhinella arenarum, as a Cue for Spatial Orientation and Its Associated Brain Activity

Acoustic communication is essential for reproduction and predator avoidance in many anuran species. For example, mating calls are generally produced by males and represent a conspicuous communication signal employed during the breeding season. Although anuran mating calls have been largely studied to analyze content and phonotaxis toward choruses, they are rarely discussed as sources of information guiding spatial behavior in broader contexts. This is striking if we consider that previous studies have shown anurans to be impressive navigators. In the current study, we investigated whether terrestrial toad (Rhinella arenarum) males can use a mating call as a spatial cue to locate a water reward in a laboratory maze. Male toads could indeed learn the location of a reward guided by a mating call. This navigational ability, as indicated by c-Fos, was associated with greater neuronal activity in the telencephalic hippocampal formation (HF; also referred to in amphibians as medial pallium), the medial septum (MS), and the central amygdala (CeA). HF and MS are telencephalic structures associated with spatial navigation in mammals and other vertebrates. The CeA, by contrast, has been studied in the context of acoustic processing and communication in other amphibian species. The results are discussed in the framework of an evolutionary conserved, HF-septal spatial-cognitive network shared by amphibians and mammals.

The Neurocognitive Basis of Spatial Reorientation

The ability to recover one's bearings when lost is a skill that is fundamental for spatial navigation. We review the cognitive and neural mechanisms that underlie this ability, with the aim of linking together previously disparate findings from animal behavior, human psychology, electrophysiology, and cognitive neuroscience. Behavioral work suggests that reorientation involves two key abilities: first, the recovery of a spatial reference frame (a cognitive map) that is appropriate to the current environment; and second, the determination of one's heading and location relative to that reference frame. Electrophysiological recording studies, primarily in rodents, have revealed potential correlates of these operations in place, grid, border/boundary, and head-direction cells in the hippocampal formation. Cognitive neuroscience studies, primarily in humans, suggest that the perceptual inputs necessary for these operations are processed by neocortical regions such as the retrosplenial complex, occipital place area and parahippocampal place area, with the retrosplenial complex mediating spatial transformations between the local environment and the recovered spatial reference frame, the occipital place area supporting perception of local boundaries, and the parahippocampal place area processing visual information that is essential for identification of the local spatial context. By combining results across these various literatures, we converge on a unified account of reorientation that bridges the cognitive and neural domains.

The orientation of homing pigeons (Columba livia f.d.) with and without navigational experience in a two-dimensional environment

Homing pigeons are known for their excellent homing ability, and their brains seem to be functionally adapted to homing. It is known that pigeons with navigational experience show a larger hippocampus and also a more lateralised brain than pigeons without navigational experience. So we hypothesized that experience may have an influence also on orientation ability. We examined two groups of pigeons (11 with navigational experience and 17 without) in a standard operant chamber with a touch screen monitor showing a 2-D schematic of a rectangular environment (as “geometric” information) and one uniquely shaped and colored feature in each corner (as “landmark” information). Pigeons were trained first for pecking on one of these features and then we examined their ability to encode geometric and landmark information in four tests by modifying the rectangular environment. All tests were done under binocular and monocular viewing to test hemispheric dominance. The number of pecks was counted for analysis. Results show that generally both groups orientate on the basis of landmarks and the geometry of environment, but landmark information was preferred. Pigeons with navigational experience did not perform better on the tests but showed a better conjunction of the different kinds of information. Significant differences between monocular and binocular viewing were detected particularly in pigeons without navigational experience on two tests with reduced information. Our data suggest that the conjunction of geometric and landmark information might be integrated after processing separately in each hemisphere and that this process is influenced by experience.

Neuronal diversity and their spine density in the hippocampal complex of the House Crow (Corvus splendens), a food-storing bird

Hippocampus, one of the parts included in the limbic system, is involved in various functions such as learning, memory, food-storing behavior, and sexual discrimination. Neuronal classes of the hippocampal complex in food-storing birds have been also reported, but the study lacks details pertaining to neuronal characteristics and the spine density of the neurons in different subfields of the hippocampus. Hence, the present study was undertaken with the aim to explore the morphology of neurons and the spines present on their dendrites within the hippocampal complex of the House Crow (Corvus splendens Vieillot, 1817), a food-storing Indian bird, and to compare it with previously reported nonfood-storing bird species. It was observed that the hippocampus of C. splendens harbors diverse neuronal classes with substantial percentages of pyramidal neurons, well-developed local circuit neurons, and high spine density. All these neuronal specializations in C. splendens can be related with the food-storing behavior of the bird, which itself is an advantage over nonfood-storing birds.

Framing the grid: effect of boundaries on grid cells and navigation

Cells in the mammalian hippocampal formation subserve neuronal representations of environmental location and support navigation in familiar environments. Grid cells constitute one of the main cell types in the hippocampal formation and are widely believed to represent a universal metric of space independent of external stimuli. Recent evidence showing that grid symmetry is distorted in non-symmetrical environments suggests that a re-examination of this hypothesis is warranted. In this review we will discuss behavioural and physiological evidence for how environmental shape and in particular enclosure boundaries influence grid cell firing properties. We propose that grid cells encode the geometric layout of enclosures.

Dissecting the Geometric Module

Disoriented children can use geometric information in combination with featural information to reorient themselves in large but not in small spaces; somewhat similar effects have been found in nonhuman animals. These results call for an explanation. We trained young chicks to reorient to find food in a corner of a small or a large rectangular room with a distinctive featural cue (a blue wall)—a task similar to that used with children. Then we tested the chicks after displacement of the feature to an adjacent wall. In the large enclosure, chicks chose the corner that maintained the correct arrangement of the featural cue with respect to sense, whereas in the small enclosure, they chose the corner that maintained the correct metrical arrangement of the walls with respect to sense. On the basis of these findings, we propose a simple model that can explain the effects of room size on spatial reorientation.

Geometric and featural systems, separable and combined: Evidence from reorientation in people with Williams syndrome

Spatial reorientation by humans and other animals engages geometric representations of surface layouts as well as featural landmarks; however, the two types of information are thought to be behaviorally and neurally separable. In this paper, we examine the use of these two types of information during reorientation among children and adults with Williams syndrome (WS), a genetic disorder accompanied by abnormalities in brain regions that support use of both geometry and landmarks. Previous studies of reorientation in adolescents and adults with WS have shown deficits in the ability to use geometry for reorientation, but intact ability to use features, suggesting that the two systems can be differentially impaired by genetic disorder. Using a slightly modified layout, we found that many WS participants could use geometry, and most could use features along with geometry. However, the developmental trajectories for the two systems were quite different from one other, and different from those found in typical development. Purely geometric responding was not correlated with age in WS, and search processes appeared similar to those in typically developing (TD) children. In contrast, use of features in combination with geometry was correlated with age in WS, and search processes were distinctly different from TD children. The results support the view that use of geometry and features stem from different underlying mechanisms, that the developmental trajectories and operation of each are altered in WS, and that combination of information from the two systems is atypical. Given brain abnormalities in regions supporting the two kinds of information, our findings suggest that the co-operation of the two systems is functionally altered in this genetic syndrome.

Seasonal dynamics within the neurons of the hippocampus in adult female Indian Ring neck Parrots (Psittacula krameri) and Asian Koels (Eudynamys scolopaceus)

In birds, a narrow strip of tissue found on the dorsomedial surface of the telencephalon and separated from the rest of the hemisphere by a ventricle is termed the hippocampal complex. Two neurohistological techniques, namely the cresyl-violet method and the Golgi–Colonnier technique, have been employed in the present study to observe seasonal dynamics within the neuronal classes of hippocampus in female Indian Ring neck Parrots (Psittacula krameri (Scopoli, 1769)) and Asian Koels (Eudynamys scolopaceus (L., 1758)). Hippocampus is known to play a central role in a variety of behaviors such as homing, visual discrimination, learning, and sexual behavior. Therefore, changes in sexual behavior during the breeding period contribute to plasticity in the hippocampus in terms of fluctuations in neuronal characteristics thereby helping the bird cope with changing conditions. A significant increase in dendritic thickness, neuronal spacing, spine morphology, and spine density were identified within the hippocampal neurons during the breeding period of the studied birds. This study establishes an overall account of seasonal dynamics occurring within the neurons of all fields of the hippocampus of birds in terms of increased dendritic thickness, spine density, spine morphology, and neuronal spacing thereby favoring the view that morphological fluctuations in neuronal characteristics during the breeding period are likely to have consequences for hippocampal neuronal function.

Reorienting with terrain slope and landmarks

Orientation (or reorientation) is the first step in navigation, because establishing a spatial frame of reference is essential for a sense of location and heading direction. Recent research on nonhuman animals has revealed that the vertical component of an environment provides an important source of spatial information, in both terrestrial and aquatic settings. Nonetheless, humans show large individual and sex differences in the ability to use terrain slope for reorientation. To understand why some participants--mainly women--exhibit a difficulty with slope, we tested reorientation in a richer environment than had been used previously, including both a tilted floor and a set of distinct objects that could be used as landmarks. This environment allowed for the use of two different strategies for solving the task, one based on directional cues (slope gradient) and one based on positional cues (landmarks). Overall, rather than using both cues, participants tended to focus on just one. Although men and women did not differ significantly in their encoding of or reliance on the two strategies, men showed greater confidence in solving the reorientation task. These facts suggest that one possible cause of the female difficulty with slope might be a generally lower spatial confidence during reorientation.

Making a stronger case for comparative research to investigate the behavioral and neurological bases of three-dimensional navigation

The rich diversity of avian natural history provides exciting possibilities for comparative research aimed at understanding three-dimensional navigation. We propose some hypotheses relating differences in natural history to potential behavioral and neurological adaptations possessed by contrasting bird species. This comparative approach may offer unique insights into some of the important questions raised by Jeffery et al.

Core knowledge of object, number, and geometry: a comparative and neural approach

Studies on the ontogenetic origins of human knowledge provide evidence for a small set of separable systems of core knowledge dealing with the representation of inanimate and animate objects, number, and geometry. Because core knowledge systems are evolutionarily ancient, they can be investigated from a comparative perspective, making use of various animal models. In this review, I discuss evidence showing precocious abilities in nonhuman species to represent (a) objects that move partly or fully out of view and their basic mechanical properties such as solidity, (b) the cardinal and ordinal/sequential aspects of numerical cognition and rudimentary arithmetic with small numerosities, and (c) the geometrical relationships among extended surfaces in the surrounding layout. Controlled rearing studies suggest that the abilities associated with core knowledge systems of objects, number, and geometry are observed in animals in the absence (or with very reduced) experience, supporting a nativistic foundation of such cognitive mechanisms. Animal models also promise a fresh approach to the issue of the neurobiological and genetic mechanisms underlying the expression of core knowledge systems.

Spatial reorientation by geometry with freestanding objects and extended surfaces: a unifying view

The macroscopic, three-dimensional surface layout geometry of an enclosure apparently provides a different contribution for spatial reorientation than the geometric cues associated with freestanding objects arranged in arrays with similar geometric shape. Here, we showed that a unitary spatial representation can account for the capability of animals to reorient both by extended surfaces and discrete objects in a small-scale spatial task. We trained domestic chicks to locate a food-reward from an opening on isolated cylinders arranged either in a geometrically uninformative (square-shaped) or informative (rectangular-shaped) arrays. The arrays were located centrally within a rectangular-shaped enclosure. Chicks trained to access the reward from a fixed position of openings proved able to reorient according to the geometric cues specified by the shape of the enclosure in all conditions. Chicks trained in a fixed position of opening with geometric cues provided both by the arena and the array proved able to reorient according to each shape separately. However, chicks trained to access the reward from a variable position of openings failed to reorient. The results suggest that the physical constrains associated with the presence of obstacles in a scene, rather than their apparent visual extension, are crucial for spatial reorientation.

Brain expression and song regulation of the cholecystokinin gene in the zebra finch (Taeniopygia guttata)

The gene encoding cholecystokinin (Cck) is abundantly expressed in the mammalian brain and has been associated with such functions as feeding termination and satiety, locomotion and self-stimulation, the modulation of anxiety-like behaviors, and learning and memory. Here we describe the brain expression and song regulation of Cck in the brain of the adult male zebra finch (Taeniopygia guttata), a songbird species. Using in situ hybridization we demonstrate that Cck is highly expressed in several discrete brain regions, most prominently the caudalmost portion of the hippocampal formation, the caudodorsal nidopallial shelf and the caudomedial nidopallium (NCM), the core or shell regions of dorsal thalamic nuclei, dopaminergic cell groups in the mesencephalon and pons, the principal nucleus of the trigeminal nerve, and the dorsal raphe. Cck was largely absent in song control system, a group of nuclei required for vocal learning and song production in songbirds, although sparse labeling was detected throughout the striatum, including song nucleus area X. We also show that levels of Cck mRNA and the number of labeled cells increase in the NCM of males and females following auditory stimulation with conspecific song. Double labeling further reveals that the majority of Cck cells, excluding those in the reticular nucleus of the thalamus, are non-GABAergic. Together, these data provide the first comprehensive characterization of Cck expression in a songbird, and suggest a possible involvement of Cck regulation in important aspects of birdsong biology, such as perceptual processing, auditory memorization, and/or vocal-motor control of song production.

GluR2/3 label expression of the AMPA-type glutamate receptor in the hippocampal formation of the homing pigeon stabilizes just after birth

The compositions of the glutamate AMPA-type receptors influence the neural response and the subunits GluR2/3 has been referred to as essential for receptor trafficking and synapse consolidation. We investigate the GluR2/3 occurrence and expression in the hippocampal formation of newly born homing pigeons by a semi-quantitative approach, the Western-blotting technique and by immunohistochemistry. Immunoreactivity for GluR2/3 occurs before hatching has been evident in neuropil that was fully dispersed over the hippocampus proper (HP) and the area parahippocampalis (APH). Although many HP cells are NeuN-positives, a specific neuronal protein indicating that they are already differentiated as neurons while not one contains GluR2/3 at the hatching day (P0). Few neurons at the APH seem to express GluR2/3 at P0, but 3 days later (P3) the GluR2/3 labeling can be recognized in many HP neurons, showing a distribution pattern that resembles the adult, gradually increasing in intensity until P10. Also, the Western-blot shows an augment between P0 and P3, remaining stable after that. The enhancement of the neuronal label at P3 coincides with the retraction of the GluR2/3 label in neuropil, reducing their occurrence during the maturational period to become restricted to the dorsomedial portion as reported for adults. As the HP GluR2/3-containing cells are supposedly projecting neurons, taking together, the results signalize the relevance of the GluR2/3 in post-hatch formation of avian hippocampal circuitry in which the third day seems to be the critical period.

Impaired geometric reorientation caused by genetic defect

The capacity to reorient in one's environment is a fundamental part of the spatial cognitive systems of both humans and nonhuman species. Abundant literature has shown that human adults and toddlers, rats, chicks, and fish accomplish reorientation through the construction and use of geometric representations of surrounding layouts, including the lengths of surfaces and their intersection. Does the development of this reorientation system rely on specific genes and their action in brain development? We tested reorientation in individuals who have Williams syndrome (WS), a genetic disorder that results in abnormalities of hippocampal and parietal areas of the brain known to be involved in reorientation. We found that in a rectangular chamber devoid of surface feature information, WS individuals do not use the geometry of the chamber to reorient, failing to find a hidden object. The failure among people with WS cannot be explained by more general deficits in visual-spatial working memory, as the same individuals performed at ceiling in a similar task in which they were not disoriented. We also found that performance among people with WS improves in a rectangular chamber with one blue wall, suggesting that some individuals with WS can use the blue wall feature to locate the hidden object. These results show that the geometric system used for reorientation in humans can be selectively damaged by specific genetic and neural abnormalities in humans.

Neurobiology of the homing pigeon--a review

Homing pigeons are well known as good homers, and the knowledge of principal parameters determining their homing behaviour and the neurological basis for this have been elucidated in the last decades. Several orientation mechanisms and parameters-sun compass, earth's magnetic field, olfactory cues, visual cues-are known to be involved in homing behaviour, whereas there are still controversial discussions about their detailed function and their importance. This paper attempts to review and summarise the present knowledge about pigeon homing by describing the known orientation mechanisms and factors, including their pros and cons. Additionally, behavioural features like motivation, experience, and track preferences are discussed. All behaviour has its origin in the brain and the neuronal basis of homing and the neuroanatomical particularities of homing pigeons are a main topic of this review. Homing pigeons have larger brains in comparison to other non-homing pigeon breeds and particularly show increased size of the hippocampus. This underlines our hypothesis that there is a relationship between hippocampus size and spatial ability. The role of the hippocampus in homing and its plasticity in response to navigational experience are discussed in support of this hypothesis.

Doing Socrates experiment right: controlled rearing studies of geometrical knowledge in animals

The issue of whether encoding of geometric information for navigational purposes crucially depends on environmental experience or whether it is innately predisposed in the brain has been recently addressed in controlled rearing studies. Non-human animals can make use of the geometric shape of an environment for spatial reorientation and in some circumstances reliance on purely geometric information (metric properties and sense) can overcome use of local featural information. Animals reared in home cages of different geometric shapes proved to be equally capable of learning and performing navigational tasks based on geometric information. The findings suggest that effective use of geometric information for spatial reorientation does not require experience in environments with right angles and metrically distinct surfaces.

Spatial representation across species: geometry, language, and maps

We review growing evidence that the reorientation system-shared by both humans and nonhuman species-privileges geometric representations of space and exhibits many of the characteristic features of modular systems. We also review evidence showing that humans can move beyond the limits of nonhuman species by using two cultural constructions, language and explicit maps. We argue that, although both of these constructions are uniquely human means of enriching the spatial system we share with other species, their representational formats, functions, and developmental trajectories are quite different, yielding distinctly different tools for empowering human spatial cognition.The capacity to reorient using geometry is present in humans by the age of 18 months.

What is the mammalian dentate gyrus good for?

In the mammalian hippocampus, the dentate gyrus (DG) is characterized by sparse and powerful unidirectional projections to CA3 pyramidal cells, the so-called mossy fibers (MF). The MF form a distinct type of synapses, rich in zinc, that appear to duplicate, in terms of the information they convey, what CA3 cells already receive from entorhinal cortex layer II cells, which project both to the DG and to CA3. Computational models have hypothesized that the function of the MF is to enforce a new, well-separated pattern of activity onto CA3 cells, to represent a new memory, prevailing over the interference produced by the traces of older memories already stored on CA3 recurrent collateral connections. Although behavioral observations support the notion that the MF are crucial for decorrelating new memory representations from previous ones, a number of findings require that this view be reassessed and articulated more precisely in the spatial and temporal domains. First, neurophysiological recordings indicate that the very sparse dentate activity is concentrated on cells that display multiple but disorderly place fields, unlike both the single fields typical of CA3 and the multiple regular grid-aligned fields of medial entorhinal cortex. Second, neurogenesis is found to occur in the adult DG, leading to new cells that are functionally added to the existing circuitry, and may account for much of its ongoing activity. Third, a comparative analysis suggests that only mammals have evolved a DG, despite some of its features being present also in reptiles, whereas the avian hippocampus seems to have taken a different evolutionary path. Thus, we need to understand both how the mammalian dentate operates, in space and time, and whether evolution, in other vertebrate lineages, has offered alternative solutions to the same computational problems.

Lateralized cognition: Asymmetrical and complementary strategies of pigeons during discrimination of the “human concept”

This study was aimed at revealing which cognitive processes are lateralized in visual categorizations of "humans" by pigeons. To this end, pigeons were trained to categorize pictures of humans and then tested binocularly or monocularly (left or right eye) on the learned categorization and for transfer to novel exemplars (Experiment 1). Subsequent tests examined whether they relied on memorized features or on a conceptual strategy, using stimuli composed of new combinations of familiar and novel humans and backgrounds (Experiment 2), whether the hemispheres processed global or local information, using pictures with different levels of scrambling (Experiment 3), and whether they attended to configuration, using distorted human figures (Experiment 4). The results suggest that the left hemisphere employs a category strategy and concentrates on local features, while the right hemisphere uses an exemplar strategy and relies on configuration. These cognitive dichotomies of the cerebral hemispheres are largely shared by humans, suggesting that lateralized cognitive systems already defined the neural architecture of the common ancestor of birds and mammals.