The avian 'prefrontal cortex' and cognition

Does a Vertebrate Morphotype of Pallial Subdivisions Really Exist?

BACKGROUND

Comparative neuroanatomists have long sought to determine which part of the pallium in nonmammals is homologous to the mammalian neocortex. A number of similar connectivity patterns across species have led to the idea that the basic organization of the vertebrate brain is relatively conserved; thus, efforts of the last decades have been focused on determining a vertebrate "morphotype" - a model comprising the characteristics believed to have been present in the last common ancestor of all vertebrates.

SUMMARY

The endeavor to determine the vertebrate morphotype has been riddled with controversies due to the extensive morphological diversity of the pallium among vertebrate taxa. Nonetheless, most proposed scenarios of pallial homology are variants of a common theme where the vertebrate pallium is subdivided into subdivisions homologous to the hippocampus, neocortex, piriform cortex, and amygdala, in a one-to-one manner. We review the rationales of major propositions of pallial homology and identify the source of the discrepancies behind different hypotheses. We consider that a source of discrepancies is the prevailing assumption that there is a single "morphotype of the pallial subdivisions" throughout vertebrates. Instead, pallial subdivisions present in different taxa probably evolved independently in each lineage.

KEY MESSAGES

We encounter discrepancies when we search for a single morphotype of subdivisions across vertebrates. These discrepancies can be resolved by considering that several subdivisions within the pallium were established after the divergence of the different lineages. The differences of pallial organization are especially remarkable between actinopterygians (including teleost fishes) and other vertebrates. Thus, the prevailing notion of a simple one-to-one homology between the mammalian and teleost pallia needs to be reconsidered.

The evolution of social play in songbirds, parrots and cockatoos - emotional or highly complex cognitive behaviour or both?

Social play has been described in many animals. However, much of this social behaviour among birds, particularly in adults, is still relatively unexplored in terms of the environmental, psychological, and social dynamics of play. This paper provides an overview of what we know about adult social play in birds and addresses areas in which subtleties and distinctions, such as in play initiation and social organisation and its relationship to expressions of play, are considered in detail. The paper considers emotional, social, innovative, and cognitive aspects of play, then the environmental conditions and affiliative bonds, suggesting a surprisingly complex framework of criteria awaiting further research. Adult social play has so far been studied in only a small number of avian species, exclusively in those with a particularly large brain relative to body size without necessarily addressing brain functions and lateralization. When lateralization of brain function is considered, it can further illuminate a possibly significant relevance of play behaviour to the evolution of cognition, to management of emotions, and the development of sociality.

Dynamic temporal neural patterns based on multichannel LFPs Identify different brain states during anesthesia in pigeons: comparison of three anesthetics

Anesthetic-induced brain activity study is crucial in avian cognitive-, consciousness-, and sleep-related research. However, the neurobiological mechanisms underlying the generation of brain rhythms and specific connectivity of birds during anesthesia are poorly understood. Although different kinds of anesthetics can be used to induce an anesthesia state, a comparison study of these drugs focusing on the neural pattern evolution during anesthesia is lacking. Here, we recorded local field potentials (LFPs) using a multi-channel micro-electrode array inserted into the nidopallium caudolateral (NCL) of adult pigeons (Columba livia) anesthetized with chloral hydrate, pelltobarbitalum natricum or urethane. Power spectral density (PSD) and functional connectivity analyses were used to measure the dynamic temporal neural patterns in NCL during anesthesia. Neural decoding analysis was adopted to calculate the probability of the pigeon's brain state and the kind of injected anesthetic. In the NCL during anesthesia, we found elevated power activity and functional connectivity at low-frequency bands and depressed power activity and connectivity at high-frequency bands. Decoding results based on the spectral and functional connectivity features indicated that the pigeon's brain states during anesthesia and the injected anesthetics can be effectively decoded. These findings provide an important foundation for future investigations on how different anesthetics induce the generation of specific neural patterns.

Changes in the dopaminergic circuitry and adult neurogenesis linked to reinforcement learning in corvids

The caudolateral nidopallium (NCL, an analog of the prefrontal cortex) is known to be involved in learning, memory, and discrimination in corvids (a songbird), whereas the involvement of other brain regions in these phenomena is not well explored. We used house crows (Corvus splendens) to explore the neural correlates of learning and decision-making by initially training them on a shape discrimination task followed by immunohistochemistry to study the immediate early gene expression (Arc), a dopaminoceptive neuronal marker (DARPP-32, Dopamine- and cAMP-regulated phosphoprotein, Mr 32 kDa) to understand the involvement of the reward pathway and an immature neuronal marker (DCX, doublecortin) to detect learning-induced changes in adult neurogenesis. We performed neuronal counts and neuronal tracing, followed by morphometric analyses. Our present results have demonstrated that besides NCL, other parts of the caudal nidopallium (NC), avian basal ganglia, and intriguingly, vocal control regions in house crows are involved in visual discrimination. We have also found that training on the visual discrimination task can be correlated with neurite pruning in mature dopaminoceptive neurons and immature DCX-positive neurons in the NC of house crows. Furthermore, there is an increase in the incorporation of new neurons throughout NC and the medial striatum which can also be linked to learning. For the first time, our results demonstrate that a combination of structural changes in mature and immature neurons and adult neurogenesis are linked to learning in corvids.

Input and Output Connections of the Crow Nidopallium Caudolaterale

The avian telencephalic structure nidopallium caudolaterale (NCL) functions as an analog to the mammalian prefrontal cortex. In crows, corvid songbirds, it plays a crucial role in higher cognitive and executive functions. These functions rely on the NCL's extensive telencephalic connections. However, systematic investigations into the brain-wide connectivity of the NCL in crows or other songbirds are lacking. Here, we studied its input and output connections by injecting retrograde and anterograde tracers into the carrion crow NCL. Our results, mapped onto a published carrion crow brain atlas, confirm NCL multisensory connections and extend prior pigeon findings by identifying a novel input from the hippocampal formation. Furthermore, we analyze crow NCL efferent projections to the arcopallium and report newly identified arcopallial neurons projecting bilaterally to the NCL. These findings help to clarify the role of the NCL as central executive hub in the corvid songbird brain.

Conscious Experience of Stimulus Presence and Absence Is Actively Encoded by Neurons in the Crow Brain

The emergence of consciousness from brain activity constitutes one of the great riddles in biology. It is commonly assumed that only the conscious perception of the presence of a stimulus elicits neuronal activation to signify a "neural correlate of consciousness," whereas the subjective experience of the absence of a stimulus is associated with a neuronal resting state. Here, we demonstrate that the two subjective states "stimulus present" and "stimulus absent" are represented by two specialized neuron populations in crows, corvid birds. We recorded single-neuron activity from the nidopallium caudolaterale of crows trained to report the presence or absence of images presented near the visual threshold. Because of the task design, neuronal activity tracking the conscious "present" versus "absent" percept was dissociated from that involved in planning a motor response. Distinct neuron populations signaled the subjective percepts of "present" and "absent" by increases in activation. The response selectivity of these two neuron populations was similar in strength and time course. This suggests a balanced code for subjective "presence" versus "absence" experiences, which might be beneficial when both conscious states need to be maintained active in the service of goal-directed behavior.

Acute Aromatase Inhibition Impairs Neural and Behavioral Auditory Scene Analysis in Zebra Finches

Auditory perception can be significantly disrupted by noise. To discriminate sounds from noise, auditory scene analysis (ASA) extracts the functionally relevant sounds from acoustic input. The zebra finch communicates in noisy environments. Neurons in their secondary auditory pallial cortex (caudomedial nidopallium, NCM) can encode song from background chorus, or scenes, and this capacity may aid behavioral ASA. Furthermore, song processing is modulated by the rapid synthesis of neuroestrogens when hearing conspecific song. To examine whether neuroestrogens support neural and behavioral ASA in both sexes, we retrodialyzed fadrozole (aromatase inhibitor, FAD) and recorded in vivo awake extracellular NCM responses to songs and scenes. We found that FAD affected neural encoding of songs by decreasing responsiveness and timing reliability in inhibitory (narrow-spiking), but not in excitatory (broad-spiking) neurons. Congruently, FAD decreased neural encoding of songs in scenes for both cell types, particularly in females. Behaviorally, we trained birds using operant conditioning and tested their ability to detect songs in scenes after administering FAD orally or injected bilaterally into NCM. Oral FAD increased response bias and decreased correct rejections in females, but not in males. FAD in NCM did not affect performance. Thus, FAD in the NCM impaired neuronal ASA but that did not lead to behavioral disruption suggesting the existence of resilience or compensatory responses. Moreover, impaired performance after systemic FAD suggests involvement of other aromatase-rich networks outside the auditory pathway in ASA. This work highlights how transient estrogen synthesis disruption can modulate higher-order processing in an animal model of vocal communication.

Enhanced Hippocampus-Nidopallium Caudolaterale Interaction in Visual-Spatial Associative Learning of Pigeons

Learning the spatial location associated with visual cues in the environment is crucial for survival. This ability is supported by a distributed interactive network. However, it is not fully understood how the most important task-related brain areas in birds, the hippocampus (Hp) and the nidopallium caudolaterale (NCL), interact in visual-spatial associative learning. To investigate the mechanisms of such coordination, synchrony and causal analysis were applied to the local field potentials of the Hp and NCL of pigeons while performing a visual-spatial associative learning task. The results showed that, over the course of learning, theta-band (4-12 Hz) oscillations in the Hp and NCL became strongly synchronized before the pigeons entered the critical choice platform for turning, with the information flowing preferentially from the Hp to the NCL. The learning process was primarily associated with the increased Hp-NCL interaction of theta rhythm. Meanwhile, the enhanced theta-band Hp-NCL interaction predicted the correct choice, supporting the pigeons' use of visual cues to guide navigation. These findings provide insight into the dynamics of Hp-NCL interaction during visual-spatial associative learning, serving to reveal the mechanisms of Hp and NCL coordination during the encoding and retrieval of visual-spatial associative memory.

Different ways of evolving tool-using brains in teleosts and amniotes

In mammals and birds, tool-using species are characterized by their relatively large telencephalon containing a higher proportion of total brain neurons compared to other species. Some teleost species in the wrasse family have evolved tool-using abilities. In this study, we compared the brains of tool-using wrasses with various teleost species. We show that in the tool-using wrasses, the telencephalon and the ventral part of the forebrain and midbrain are significantly enlarged compared to other teleost species but do not contain a larger proportion of cells. Instead, this size difference is due to large fiber tracts connecting the dorsal part of the telencephalon (pallium) to the inferior lobe, a ventral mesencephalic structure absent in amniotes. The high degree of connectivity between these structures in tool-using wrasses suggests that the inferior lobe could contribute to higher-order cognitive functions. We conclude that the evolution of non-telencephalic structures might have been key in the emergence of these cognitive functions in teleosts.

Convergent Circuit Computation for Categorization in the Brains of Primates and Songbirds

Categorization is crucial for behavioral flexibility because it enables animals to group stimuli into meaningful classes that can easily be generalized to new circumstances. A most abstract quantitative category is set size, the number of elements in a set. This review explores how categorical number representations are realized by the operations of excitatory and inhibitory neurons in associative telencephalic microcircuits in primates and songbirds. Despite the independent evolution of the primate prefrontal cortex and the avian nidopallium caudolaterale, the neuronal computations of these associative pallial circuits show surprising correspondence. Comparing cellular functions in distantly related taxa can inform about the evolutionary principles of circuit computations for cognition in distinctly but convergently realized brain structures.

Association neurons in the crow telencephalon link visual signs to numerical values

Many animals can associate signs with numerical values and use these signs in a goal-directed way during task performance. However, the neuronal basis of this semantic association has only rarely been investigated, and so far only in primates. How mechanisms of number associations are implemented in the distinctly evolved brains of other animal taxa such as birds is currently unknown. Here, we explored this semantic number-sign mapping by recording single-neuron activity in the crows' nidopallium caudolaterale (NCL), a brain structure critically involved in avian numerical cognition. Crows were trained to associate visual shapes with varying numbers of items in a number production task. The responses of many NCL neurons during stimulus presentation reflected the numerical values associated with visual shapes in a behaviorally relevant way. Consistent with the crow's better behavioral performance with signs, neuronal representations of numerical values extracted from shapes were more selective compared to those from dot arrays. The existence of number association neurons in crows points to a phylogenetic preadaptation of the brains of cognitively advanced vertebrates to link visual shapes with numerical meaning.

The prefrontal cortex of the bottlenose dolphin (Tursiops truncatus Montagu, 1821): a tractography study and comparison with the human

Cetaceans are well known for their remarkable cognitive abilities including self-recognition, sound imitation and decision making. In other mammals, the prefrontal cortex (PFC) takes a key role in such cognitive feats. In cetaceans, however, a PFC could up to now not be discerned based on its usual topography. Classical in vivo methods like tract tracing are legally not possible to perform in Cetacea, leaving diffusion-weighted imaging (DWI) as the most viable alternative. This is the first investigation focussed on the identification of the cetacean PFC homologue. In our study, we applied the constrained spherical deconvolution (CSD) algorithm on 3 T DWI scans of three formalin-fixed brains of bottlenose dolphins (Tursiops truncatus) and compared the obtained results to human brains, using the same methodology. We first identified fibres related to the medio-dorsal thalamic nuclei (MD) and then seeded the obtained putative PFC in the dolphin as well as the known PFC in humans. Our results outlined the dolphin PFC in areas not previously studied, in the cranio-lateral, ectolateral and opercular gyri, and furthermore demonstrated a similar connectivity pattern between the human and dolphin PFC. The antero-lateral rotation of the PFC, like in other areas, might be the result of the telescoping process which occurred in these animals during evolution.

American crows that excel at tool use activate neural circuits distinct from less talented individuals

Tools enable animals to exploit and command new resources. However, the neural circuits underpinning tool use and how neural activity varies with an animal's tool proficiency, are only known for humans and some other primates. We use 18F-fluorodeoxyglucose positron emission tomography to image the brain activity of naïve vs trained American crows (Corvus brachyrhynchos) when presented with a task requiring the use of stone tools. As in humans, talent affects the neural circuits activated by crows as they prepare to execute the task. Naïve and less proficient crows use neural circuits associated with sensory- and higher-order processing centers (the mesopallium and nidopallium), while highly proficient individuals increase activity in circuits associated with motor learning and tactile control (hippocampus, tegmentum, nucleus basorostralis, and cerebellum). Greater proficiency is found primarily in adult female crows and may reflect their need to use more cognitively complex strategies, like tool use, to obtain food.

Reward history modulates visual attention in an avian model

Attention can be biased towards previously reward-associated stimuli even when they are task-irrelevant and physically non-salient, although studies of reward-modulated attention have been largely limited to primate (including human and nonhuman) models. Birds have been shown to have the capacity to discriminate reward and spatial cues in a manner similar to primates, but whether reward history involuntarily affects their attention in the same way remains unclear. We adapted a spatial cueing paradigm with differential rewards to investigate how reward modulates the allocation of attention in peafowl (Pavo cristatus). The birds were required to locate and peck a target on a computer screen that was preceded by a high-value or low-value color cue that was uninformative with respect to the location of the upcoming target. All birds exhibited a validity effect (performance enhanced on valid compared to invalid cue), and an interaction effect between value and validity was evident at the group level, being particularly pronounced in the birds with the greatest amount of reward training. The time course of reward learning was conspicuously incremental, phenomenologically slower compared to primates. Our findings suggest a similar influence of reward history on attention across phylogeny despite a significant difference in neuroanatomy.

Wolf-Dog-Human: Companionship Based on Common Social Tools

Wolves, dogs and humans share extremely social and cooperative minds. These similarities are rooted in phylogenetic homology and in the convergence of neuronal and physiological mechanisms, particularly the brain, in the functioning and communication of basic affects and in the mechanisms of stress and calming. The domesticated wolves called dogs are particularly close companion animals. Both Palaeolithic humans and wolves were hypercursorial hunters, cooperating in complex and prosocial ways within their clans with respect to hunting, raising offspring, and defending against conspecific and heterospecific competitors and predators. These eco-social parallels have shaped the development of similar social mindsets in wolves and humans. Over the millennia of domestication, this social match was fine-tuned, resulting in the socio-cognitive specialists humans and dogs, possessing amazingly similar social brains and minds. Therefore, it can be concluded that the quality of their relationships with their human masters is a major factor in the wellbeing, welfare and even health of dogs, as well as in the wellbeing of their human partners. Based on their strikingly similar social brains and physiologies, it can be further concluded that anthropomorphically applying human empathy to dogs in an educated manner may not be as inappropriate as previously thought.

Molecular biology of serotonergic systems in avian brains

Serotonin (5-hydroxytryptamine, 5-HT) is a phylogenetically conserved neurotransmitter and modulator. Neurons utilizing serotonin have been identified in the central nervous systems of all vertebrates. In the central serotonergic system of vertebrate species examined so far, serotonergic neurons have been confirmed to exist in clusters in the brainstem. Although many serotonin-regulated cognitive, behavioral, and emotional functions have been elucidated in mammals, equivalents remain poorly understood in non-mammalian vertebrates. The purpose of this review is to summarize current knowledge of the anatomical organization and molecular features of the avian central serotonergic system. In addition, selected key functions of serotonin are briefly reviewed. Gene association studies between serotonergic system related genes and behaviors in birds have elucidated that the serotonergic system is involved in the regulation of behavior in birds similar to that observed in mammals. The widespread distribution of serotonergic modulation in the central nervous system and the evolutionary conservation of the serotonergic system provide a strong foundation for understanding and comparing the evolutionary continuity of neural circuits controlling corresponding brain functions within vertebrates. The main focus of this review is the chicken brain, with this type of poultry used as a model bird. The chicken is widely used not only as a model for answering questions in developmental biology and as a model for agriculturally useful breeding, but also in research relating to cognitive, behavioral, and emotional processes. In addition to a wealth of prior research on the projection relationships of avian brain regions, detailed subdivision similarities between avian and mammalian brains have recently been identified. Therefore, identifying the neural circuits modulated by the serotonergic system in avian brains may provide an interesting opportunity for detailed comparative studies of the function of serotonergic systems in mammals.

Dim artificial light at night alters immediate early gene expression throughout the avian brain

Artificial light at night (ALAN) is a pervasive pollutant that alters physiology and behavior. However, the underlying mechanisms triggering these alterations are unknown, as previous work shows that dim levels of ALAN may have a masking effect, bypassing the central clock. Light stimulates neuronal activity in numerous brain regions which could in turn activate downstream effectors regulating physiological response. In the present study, taking advantage of immediate early gene (IEG) expression as a proxy for neuronal activity, we determined the brain regions activated in response to ALAN. We exposed zebra finches to dim ALAN (1.5 lux) and analyzed 24 regions throughout the brain. We found that the overall expression of two different IEGs, cFos and ZENK, in birds exposed to ALAN were significantly different from birds inactive at night. Additionally, we found that ALAN-exposed birds had significantly different IEG expression from birds inactive at night and active during the day in several brain areas associated with vision, movement, learning and memory, pain processing, and hormone regulation. These results give insight into the mechanistic pathways responding to ALAN that underlie downstream, well-documented behavioral and physiological changes.

Mapping of corticotropin-releasing factor, receptors, and binding protein mRNA in the chicken telencephalon throughout development

Understanding the neural mechanisms that regulate the stress response is critical to know how animals adapt to a changing world and is one of the key factors to be considered for improving animal welfare. Corticotropin-releasing factor (CRF) is crucial for regulating physiological and endocrine responses, triggering the activation of the sympathetic nervous system and the hypothalamo-pituitary-adrenal axis (HPA) during stress. In mammals, several telencephalic areas, such as the amygdala and the hippocampus, regulate the autonomic system and the HPA responses. These centers include subpopulations of CRF containing neurons that, by way of CRF receptors, play modulatory roles in the emotional and cognitive aspects of stress. CRF binding protein also plays a role, buffering extracellular CRF and regulating its availability. CRF role in activation of the HPA is evolutionary conserved in vertebrates, highlighting the relevance of this system to help animals cope with adversity. However, knowledge on CRF systems in the avian telencephalon is very limited, and no information exists on detailed expression of CRF receptors and binding protein. Knowing that the stress response changes with age, with important variations during the first week posthatching, the aim of this study was to analyze mRNA expression of CRF, CRF receptors 1 and 2, and CRF binding protein in chicken telencephalon throughout embryonic and early posthatching development, using in situ hybridization. Our results demonstrate an early expression of CRF and its receptors in pallial areas regulating sensory processing, sensorimotor integration and cognition, and a late expression in subpallial areas regulating the stress response. However, CRF buffering system develops earlier in the subpallium than in the pallium. These results help to understand the mechanisms underlying the negative effects of noise and light during prehatching stages in chicken, and suggest that stress regulation becomes more sophisticated with age.

Connectomes: from a sparsity of networks to large-scale databases

The analysis of whole brain networks started in the 1980s when only a handful of connectomes were available. In these early days, information about the human connectome was absent and one could only dream about having information about connectivity in a single human subject. Thanks to non-invasive methods such as diffusion imaging, we now know about connectivity in many species and, for some species, in many individuals. To illustrate the rapid change in availability of connectome data, the UK Biobank is on track to record structural and functional connectivity in 100,000 human subjects. Moreover, connectome data from a range of species is now available: from Caenorhabditis elegans and the fruit fly to pigeons, rodents, cats, non-human primates, and humans. This review will give a brief overview of what structural connectivity data is now available, how connectomes are organized, and how their organization shows common features across species. Finally, I will outline some of the current challenges and potential future work in making use of connectome information.

Categorical representation of abstract spatial magnitudes in the executive telencephalon of crows

The ability to group abstract continuous magnitudes into meaningful categories is cognitively demanding but key to intelligent behavior. To explore its neuronal mechanisms, we trained carrion crows to categorize lines of variable lengths into arbitrary "short" and "long" categories. Single-neuron activity in the nidopallium caudolaterale (NCL) of behaving crows reflected the learned length categories of visual stimuli. The length categories could be reliably decoded from neuronal population activity to predict the crows' conceptual decisions. NCL activity changed with learning when a crow was retrained with the same stimuli assigned to more categories with new boundaries ("short", "medium," and "long"). Categorical neuronal representations emerged dynamically so that sensory length information at the beginning of the trial was transformed into behaviorally relevant categorical representations shortly before the crows' decision making. Our data show malleable categorization capabilities for abstract spatial magnitudes mediated by the flexible networks of the crow NCL.

Multi-channel recordings reveal age-related differences in the sleep of juvenile and adult zebra finches

Despite their phylogenetic differences and distinct pallial structures, mammals and birds show similar electroencephalography (EEG) traces during sleep, consisting of distinct rapid eye movement (REM) sleep and slow wave sleep (SWS) stages. Studies in human and a limited number of other mammalian species show that this organization of sleep into interleaving stages undergoes radical changes during lifetime. Do these age-dependent variations in sleep patterns also occur in the avian brain? Does vocal learning have an effect on sleep patterns in birds? To answer these questions, we recorded multi-channel sleep EEG from juvenile and adult zebra finches for several nights. Whereas adults spent more time in SWS and REM sleep, juveniles spent more time in intermediate sleep (IS). The amount of IS was significantly larger in male juveniles engaged in vocal learning compared to female juveniles, which suggests that IS could be important for vocal learning. In addition, we observed that functional connectivity increased rapidly during maturation of young juveniles, and was stable or declined at older ages. Synchronous activity during sleep was larger for recording sites in the left hemisphere for both juveniles and adults, and generally intra-hemispheric synchrony was larger than inter-hemispheric synchrony during sleep. A graph theory analysis revealed that in adults, highly correlated EEG activity tended to be distributed across fewer networks that were spread across a wider area of the brain, whereas in juveniles, highly correlated EEG activity was distributed across more numerous, albeit smaller, networks in the brain. Overall, our results reveal that significant changes occur in the neural signatures of sleep during maturation in an avian brain.

Goal given moment modulates the time period of gamma oscillations in nidopallium caudolaterale during the goal-directed behavior of pigeon

The cognitive processes of goal-directed navigation are believed to be organized around and serve the identification and selection of goals. Differences in LFP signals in avian nidopallium caudolaterale (NCL) under different goal location/distance information in the goal-directed behavior have been studied. However, for goals that are multifarious constructs that include various information, the modulation of goal time information on the LFP of NCL during goal-directed behavior remains unclear. In this study, we recorded the LFP activity from the NCL of eight pigeons as they performed two goal-directed decision-making tasks in a plus-maze. During the two tasks with different goal time information, spectral analysis revealed significant LFP power selectively enhanced in the slow gamma band (40-60 Hz), while the slow gamma band of LFP which could effectively decode the behavioral goal of the pigeons existed in different time periods. These findings suggest that the LFP activity in the gamma band correlates with the goal-time information, and help to shed light on the contribution of the gamma rhythm recorded from the NCL in goal-directed behavior.

Tracing development of song memory with fMRI in zebra finches after a second tutoring experience

Sensory experiences in early development shape higher cognitive functions such as language acquisition in humans and song learning in birds. Zebra finches (Taeniopygia guttata) sequentially exposed to two different song 'tutors' during the sensitive period in development are able to learn from their second tutor and eventually imitate aspects of his song, but the neural substrate involved in learning a second song is unknown. We used fMRI to examine neural activity associated with learning two songs sequentially. We found that acquisition of a second song changes lateralization of the auditory midbrain. Interestingly, activity in the caudolateral Nidopallium (NCL), a region adjacent to the secondary auditory cortex, was related to the fidelity of second-song imitation. These findings demonstrate that experience with a second tutor can permanently alter neural activity in brain regions involved in auditory perception and song learning.

Executive Control of Sequence Behavior in Pigeons Involves Two Distinct Brain Regions

Executive functions arise from multiple regions of the brain acting in concert. To facilitate such cross-regional computations, the brain is organized into distinct executive networks, like the frontoparietal network. Despite similar cognitive abilities across many domains, little is known about such executive networks in birds. Recent advances in avian fMRI have shown a possible subset of regions, including the nidopallium caudolaterale (NCL) and the lateral part of medial intermediate nidopallium (NIML), that may contribute to complex cognition, forming an action control system of pigeons. We investigated the neuronal activity of NCL and NIML. Single-cell recordings were obtained during the execution of a complex sequential motor task that required executive control to stop executing one behavior and continue with a different one. We compared the neuronal activity of NIML to NCL and found that both regions fully processed the ongoing sequential execution of the task. Differences arose from how behavioral outcome was processed. Our results indicate that NCL takes on a role in evaluating outcome, while NIML is more tightly associated with ongoing sequential steps. Importantly, both regions seem to contribute to overall behavioral output as parts of a possible avian executive network, crucial for behavioral flexibility and decision-making.

Neural correlates of cognitively controlled vocalizations in a corvid songbird

The neuronal basis of the songbird's song system is well understood. However, little is known about the neuronal correlates of the executive control of songbird vocalizations. Here, we record single-unit activity from the pallial endbrain region "nidopallium caudolaterale" (NCL) of crows that vocalize to the presentation of a visual go-cue but refrain from vocalizing during trials without a go-cue. We find that the preparatory activity of single vocalization-correlated neurons, but also of the entire population of NCL neurons, before vocal onset predicts whether or not the crows will produce an instructed vocalization. Fluctuations in baseline neuronal activity prior to the go-cue influence the premotor activity of such vocalization-correlated neurons and seemingly bias the crows' decision to vocalize. Neuronal response modulation significantly differs between volitional and task-unrelated vocalizations. This suggests that the NCL can take control over the vocal motor network during the production of volitional vocalizations in a corvid songbird.

Recent developments in parrot cognition: a quadrennial update

Psittacines, along with corvids, are commonly referred to as 'feathered apes' due to their advanced cognitive abilities. Until rather recently, the research effort on parrot cognition was lagging behind that on corvids, however current developments show that the number of parrot studies is steadily increasing. In 2018, M. L. Lambert et al. provided a comprehensive review on the status of the most important work done so far in parrot and corvid cognition. Nevertheless, only a little more than 4 years after this publication, more than 50 new parrot studies have been published, some of them chartering completely new territory. On the 25th anniversary of Animal Cognition we think this warrants a detailed review of parrot cognition research over the last 4 years. We aim to capture recent developments and current trends in this rapidly expanding and diversifying field.

Visual categories and concepts in the avian brain

Birds are excellent model organisms to study perceptual categorization and concept formation. The renewed focus on avian neuroscience has sparked an explosion of new data in the field. At the same time, our understanding of sensory and particularly visual structures in the avian brain has shifted fundamentally. These recent discoveries have revealed how categorization is mediated in the avian brain and has generated a theoretical framework that goes beyond the realm of birds. We review the contribution of avian categorization research-at the methodical, behavioral, and neurobiological levels. To this end, we first introduce avian categorization from a behavioral perspective and the common elements model of categorization. Second, we describe the functional and structural organization of the avian visual system, followed by an overview of recent anatomical discoveries and the new perspective on the avian 'visual cortex'. Third, we focus on the neurocomputational basis of perceptual categorization in the bird's visual system. Fourth, an overview of the avian prefrontal cortex and the prefrontal contribution to perceptual categorization is provided. The fifth section outlines how asymmetries of the visual system contribute to categorization. Finally, we present a mechanistic view of the neural principles of avian visual categorization and its putative extension to concept learning.

Behavioral laterality is correlated with problem-solving performance in a songbird

Cerebral lateralization, which is often reflected in an individual's behavioral laterality (e.g., handedness and footedness), may bring animals certain benefits such as enhanced cognitive performance. Although the lateralization-cognition relationship has been widely studied in humans and other animals, current evidence supporting their relationship is ambiguous and warrants additional insights from more studies. Moreover, the lateralization-cognition relationship in non-human animals has been mostly studied in human-reared populations, and investigations of wild populations are particularly scarce. Here, we test the footedness of wild-caught male yellow-bellied tits (Pardaliparus venustulus) and investigate its association with their performance in learning to solve a toothpick-pulling problem and a drawer-opening problem. The tested birds showed an overall trend to gradually spent less time solving the problems, implying that they learned to solve the problems. Left- and right-footed individuals showed no significant differences in the latency to explore the experimental apparatuses and in the proportions that completed and did not complete the tasks. However, the left-footed individuals learned faster than the right-footed individuals in the drawer-opening experiment, indicating a potential cognitive advantage associated with left-footedness. These results contribute to the understanding of the behavioral differences between differently footed individuals and, in particular, the relationship between lateralization and cognitive ability in wild animals.

Number selective sensorimotor neurons in the crow translate perceived numerosity into number of actions

Translating a perceived number into a matching number of self-generated actions is a hallmark of numerical reasoning in humans and animals alike. To explore this sensorimotor transformation, we trained crows to judge numerical values in displays and to flexibly plan and perform a matching number of pecks. We report number selective sensorimotor neurons in the crow telencephalon that signaled the impending number of self-generated actions. Neuronal population activity during the sensorimotor transformation period predicted whether the crows mistakenly planned fewer or more pecks than instructed. During sensorimotor transformation, both a static neuronal code characterized by persistently number-selective neurons and a dynamic code originating from neurons carrying rapidly changing numerical information emerged. The findings indicate there are distinct functions of abstract neuronal codes supporting the sensorimotor number system.

Motor constellation theory: A model of infants' phonological development

Every normally developing human infant solves the difficult problem of mapping their native-language phonology, but the neural mechanisms underpinning this behavior remain poorly understood. Here, motor constellation theory, an integrative neurophonological model, is presented, with the goal of explicating this issue. It is assumed that infants' motor-auditory phonological mapping takes place through infants' orosensory "reaching" for phonological elements observed in the language-specific ambient phonology, via reference to kinesthetic feedback from motor systems (e.g., articulators), and auditory feedback from resulting speech and speech-like sounds. Attempts are regulated by basal ganglion-cerebellar speech neural circuitry, and successful attempts at reproduction are enforced through dopaminergic signaling. Early in life, the pace of anatomical development constrains mapping such that complete language-specific phonological mapping is prohibited by infants' undeveloped supralaryngeal vocal tract and undescended larynx; constraints gradually dissolve with age, enabling adult phonology. Where appropriate, reference is made to findings from animal and clinical models. Some implications for future modeling and simulation efforts, as well as clinical settings, are also discussed.

A Fast and Efficient Ensemble Transfer Entropy and Applications in Neural Signals

The ensemble transfer entropy (TEensemble) refers to the transfer entropy estimated from an ensemble of realizations. Due to its time-resolved analysis, it is adapted to analyze the dynamic interaction between brain regions. However, in the traditional TEensemble, multiple sets of surrogate data should be used to construct the null hypothesis distribution, which dramatically increases the computational complexity. To reduce the computational cost, a fast, efficient TEensemble with a simple statistical test method is proposed here, in which just one set of surrogate data is involved. To validate the improved efficiency, the simulated neural signals are used to compare the characteristics of the novel TEensemble with those of the traditional TEensemble. The results show that the time consumption is reduced by two or three magnitudes in the novel TEensemble. Importantly, the proposed TEensemble could accurately track the dynamic interaction process and detect the strength and the direction of interaction robustly even in the presence of moderate noises. The novel TEensemble reaches its steady state with the increased samples, which is slower than the traditional method. Furthermore, the effectiveness of the novel TEensemble was verified in the actual neural signals. Accordingly, the TEensemble proposed in this work may provide a suitable way to investigate the dynamic interactions between brain regions.

A brain atlas of the carrion crow (Corvus corone)

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.

Awareness and consciousness in humans and animals – neural and behavioral correlates in an evolutionary perspective

Awareness or consciousness in the context of stimulus perception can directly be assessed in well controlled test situations with humans via the persons’ reports about their subjective experiences with the stimuli. Since we have no direct access to subjective experiences in animals, their possible awareness or consciousness in stimulus perception tasks has often been inferred from behavior and cognitive abilities previously observed in aware and conscious humans. Here, we analyze published human data primarily on event-related potentials and brain-wave generation during perception and responding to sensory stimuli and extract neural markers (mainly latencies of evoked-potential peaks and of gamma-wave occurrence) indicating that a person became aware or conscious of the perceived stimulus. These neural correlates of consciousness were then applied to sets of corresponding data from various animals including several species of mammals, and one species each of birds, fish, cephalopods, and insects. We found that the neural markers from studies in humans could also successfully be applied to the mammal and bird data suggesting that species in these animal groups can become subjectively aware of and conscious about perceived stimuli. Fish, cephalopod and insect data remained inconclusive. In an evolutionary perspective we have to consider that both awareness of and consciousness about perceived stimuli appear as evolved, attention-dependent options added to the ongoing neural activities of stimulus processing and action generation. Since gamma-wave generation for functional coupling of brain areas in aware/conscious states is energetically highly cost-intensive, it remains to be shown which animal species under which conditions of lifestyle and ecological niche may achieve significant advantages in reproductive fitness by drawing upon these options. Hence, we started our discussion about awareness and consciousness in animals with the question in how far these expressions of brain activity are necessary attributes for perceiving stimuli and responding in an adaptive way.

Constitutive gene expression differs in three brain regions important for cognition in neophobic and non-neophobic house sparrows (Passer domesticus)

Neophobia (aversion to new objects, food, and environments) is a personality trait that affects the ability of wildlife to adapt to new challenges and opportunities. Despite the ubiquity and importance of this trait, the molecular mechanisms underlying repeatable individual differences in neophobia in wild animals are poorly understood. We evaluated wild-caught house sparrows (Passer domesticus) for neophobia in the lab using novel object tests. We then selected a subset of neophobic and non-neophobic individuals (n = 3 of each, all females) and extracted RNA from four brain regions involved in learning, memory, threat perception, and executive function: striatum, caudal dorsomedial hippocampus, medial ventral arcopallium, and caudolateral nidopallium (NCL). Our analysis of differentially expressed genes (DEGs) used 11,889 gene regions annotated in the house sparrow reference genome for which we had an average of 25.7 million mapped reads/sample. PERMANOVA identified significant effects of brain region, phenotype (neophobic vs. non-neophobic), and a brain region by phenotype interaction. Comparing neophobic and non-neophobic birds revealed constitutive differences in DEGs in three of the four brain regions examined: hippocampus (12% of the transcriptome significantly differentially expressed), striatum (4%) and NCL (3%). DEGs included important known neuroendocrine mediators of learning, memory, executive function, and anxiety behavior, including serotonin receptor 5A, dopamine receptors 1, 2 and 5 (downregulated in neophobic birds), and estrogen receptor beta (upregulated in neophobic birds). These results suggest that some of the behavioral differences between phenotypes may be due to underlying gene expression differences in the brain. The large number of DEGs in neophobic and non-neophobic birds also implies that there are major differences in neural function between the two phenotypes that could affect a wide variety of behavioral traits beyond neophobia.

Inhibition of NLRP3 inflammasome-mediated neuroinflammation alleviates electroconvulsive shock-induced memory impairment via regulation of hippocampal synaptic plasticity in depressive rats

Electroconvulsive shock has been considered one of the most effective treatment modalities for major depressive disorder. The association of acute transitory neuroinflammation in the hippocampus following electroconvulsive therapy with transient learning and memory impairment limits its clinical application. Whereas the NLRP3 inflammatory pathway is deemed to serve a key role in neuroinflammatory regulation, we aimed to examine if NLRP3 inflammasome activation was linked to electroconvulsive shock (ECS)-induced neuroinflammation and cognitive deficits. The depressed rats were modeled with chronic unpredictable mild stress. Their depression-like behaviors and cognitive performance were evaluated via sucrose preference test, forced swim test, open field test, and Morris water maze test. The NLRP3 expression was determined by western blot. The hippocampal CA1 region was immunohistochemically and electron-microscopically examined, respectively, for the activation of Iba-1 positive microglia and the ultrastructure of synapses. In this work, we found that ECS induced microglial activation in the rat hippocampal CA1 region. Pharmacological inhibition of NLRP3 inflammasome with MCC950 (NLRP3 inhibitor) in vivo significantly alleviated ECS-induced spatial learning and memory impairment, partially reversed neuroinflammation, and synaptic structural plasticity in the damaged hippocampal CA1 region, and reduced synapse associated protein expression and microglial activation. It offers a potential new approach for the prevention and treatment of cognitive decline following electroconvulsive therapy.

Executive Functions in Birds

Executive functions comprise of top-down cognitive processes that exert control over information processing, from acquiring information to issuing a behavioral response. These cognitive processes of inhibition, working memory, and cognitive flexibility underpin complex cognitive skills, such as episodic memory and planning, which have been repeatedly investigated in several bird species in recent decades. Until recently, avian executive functions were studied in relatively few bird species but have gained traction in comparative cognitive research following MacLean and colleagues’ large-scale study from 2014. Therefore, in this review paper, the relevant previous findings are collected and organized to facilitate further investigations of these core cognitive processes in birds. This review can assist in integrating findings from avian and mammalian cognitive research and further the current understanding of executive functions’ significance and evolution.

Cell-type specific pallial circuits shape categorical tuning responses in the crow telencephalon

The nidopallium caudolaterale (NCL), an integration centre in the telencephalon of birds, plays a crucial role in representing and maintaining abstract categories and concepts. However, the computational principles allowing pallial microcircuits consisting of excitatory and inhibitory neurons to shape the tuning to abstract categories remain elusive. Here we identified the major pallial cell types, putative excitatory projection cells and inhibitory interneurons, by characterizing the waveforms of action potentials recorded in crows performing a cognitively demanding numerical categorization task. Both cell types showed clear differences in their capacity to encode categorical information. Nearby and functionally coupled putative projection neurons generally exhibited similar tuning, whereas putative interneurons showed mainly opposite tuning. The results favour feedforward mechanisms for the shaping of categorical tuning in microcircuits of the NCL. Our findings help to decipher the workings of pallial microcircuits in birds during complex cognition and to compare them vis-a-vis neocortical processes in mammals.

Neural recordings from the caudolateral nidopallium in crows during a numerosity task suggest there are two subsets of projection neurons and inhibitory interneurons involved in complex cognition.

The evolution of quantitative sensitivity

The ability to represent approximate quantities appears to be phylogenetically widespread, but the selective pressures and proximate mechanisms favouring this ability remain unknown. We analysed quantity discrimination data from 672 subjects across 33 bird and mammal species, using a novel Bayesian model that combined phylogenetic regression with a model of number psychophysics and random effect components. This allowed us to combine data from 49 studies and calculate the Weber fraction (a measure of quantity representation precision) for each species. We then examined which cognitive, socioecological and biological factors were related to variance in Weber fraction. We found contributions of phylogeny to quantity discrimination performance across taxa. Of the neural, socioecological and general cognitive factors we tested, cortical neuron density and domain-general cognition were the strongest predictors of Weber fraction, controlling for phylogeny. Our study is a new demonstration of evolutionary constraints on cognition, as well as of a relation between species-specific neuron density and a particular cognitive ability.

This article is part of the theme issue ‘Systems neuroscience through the lens of evolutionary theory’.

Neurons in the pigeon visual network discriminate between faces, scrambled faces, and sine grating images

Discriminating between object categories (e.g., conspecifics, food, potential predators) is a critical function of the primate and bird visual systems. We examined whether a similar hierarchical organization in the ventral stream that operates for processing faces in monkeys also exists in the avian visual system. We performed electrophysiological recordings from the pigeon Wulst of the thalamofugal pathway, in addition to the entopallium (ENTO) and mesopallium ventrolaterale (MVL) of the tectofugal pathway, while pigeons viewed images of faces, scrambled controls, and sine gratings. A greater proportion of MVL neurons fired to the stimuli, and linear discriminant analysis revealed that the population response of MVL neurons distinguished between the stimuli with greater capacity than ENTO and Wulst neurons. While MVL neurons displayed the greatest response selectivity, in contrast to the primate system no neurons were strongly face-selective and some responded best to the scrambled images. These findings suggest that MVL is primarily involved in processing the local features of images, much like the early visual cortex.

Neurons in the Dorso-Central Division of Zebrafish Pallium Respond to Change in Visual Numerosity

We found a region of the zebrafish pallium that shows selective activation upon change in the numerosity of visual stimuli. Zebrafish were habituated to sets of small dots that changed in individual size, position, and density, while maintaining their numerousness and overall surface. During dishabituation tests, zebrafish faced a change in number (with the same overall surface), in shape (with the same overall surface and number), or in size (with the same shape and number) of the dots, whereas, in a control group, zebrafish faced the same stimuli as during the habituation. Modulation of the expression of the immediate early genes c-fos and egr-1 and in situ hybridization revealed a selective activation of the caudal part of the dorso-central division of the zebrafish pallium upon change in numerosity. These findings support the existence of an evolutionarily conserved mechanism for approximate magnitude and provide an avenue for understanding its underlying molecular correlates.

Toward a Computational Neuroethology of Vocal Communication: From Bioacoustics to Neurophysiology, Emerging Tools and Future Directions

Recently developed methods in computational neuroethology have enabled increasingly detailed and comprehensive quantification of animal movements and behavioral kinematics. Vocal communication behavior is well poised for application of similar large-scale quantification methods in the service of physiological and ethological studies. This review describes emerging techniques that can be applied to acoustic and vocal communication signals with the goal of enabling study beyond a small number of model species. We review a range of modern computational methods for bioacoustics, signal processing, and brain-behavior mapping. Along with a discussion of recent advances and techniques, we include challenges and broader goals in establishing a framework for the computational neuroethology of vocal communication.

Gene expression profiles of the muscarinic acetylcholine receptors in brain regions relating to filial imprinting of newly-hatched domestic chicks

Muscarinic acetylcholine receptors (mAChRs) in the central nervous system play an important role in regulating complex functions such as learning, memory, and selective attention. Five subtypes of the mAChRs (M₁-M₅) have been identified in mammals, and are classified into two subfamilies: excitatory (M₁, M₃, and M₅) and inhibitory (M₂ and M₄) subfamilies. Filial imprinting of domestic chicks is a useful model in the laboratory to investigate the mechanisms of memory formation in early learning. We recently found that mAChRs in the intermediate medial mesopallium (IMM) are involved in the memory formation of imprinting. However, expression profiles of each mAChR subtype in the brain regions including the IMM remain unexplored. Here we show the unique gene expression of each mAChR subtype in the pallial regions involved in imprinting. In terms of the excitatory mAChRs, M₅ was expressed in the IMM region and other parts of the pallium, whereas M₃ was less expressed in the IMM but highly expressed in the hyperpallium and nidopallium. Regarding the inhibitory mAChRs, M₂ was sparsely distributed but clearly in some cells throughout the pallial regions. M₄ was highly expressed in the IMM region and other parts of the pallium. These expression profiles can be used as a basis for understanding cholinergic modulation in the memory formation of imprinting and other learning processes in birds, and compared to those of mammals.

Computational benefits of structural plasticity, illustrated in songbirds

The plasticity of nervous systems allows animals to quickly adapt to a changing environment. In particular, the structural plasticity of brain networks is often critical to the development of the central nervous system and the acquisition of complex behaviors. As an example, structural plasticity is central to the development of song-related brain circuits and may be critical for song acquisition in juvenile songbirds. Here, we review current evidences for structural plasticity and their significance from a computational point of view. We start by reviewing evidence for structural plasticity across species and categorizing them along the spatial axes as well as the along the time course during development. We introduce the vocal learning circuitry in zebra finches, as a useful example of structural plasticity, and use this specific case to explore the possible contributions of structural plasticity to computational models. Finally, we discuss current modeling studies incorporating structural plasticity and unexplored questions which are raised by such models.

Modelling behaviors relevant to brain disorders in the nonhuman primate: Are we there yet?

Recent years have seen a profound resurgence of activity with nonhuman primates (NHPs) to model human brain disorders. From marmosets to macaques, the study of NHP species offers a unique window into the function of primate-specific neural circuits that are impossible to examine in other models. Examining how these circuits manifest into the complex behaviors of primates, such as advanced cognitive and social functions, has provided enormous insights to date into the mechanisms underlying symptoms of numerous neurological and neuropsychiatric illnesses. With the recent optimization of modern techniques to manipulate and measure neural activity in vivo, such as optogenetics and calcium imaging, NHP research is more well-equipped than ever to probe the neural mechanisms underlying pathological behavior. However, methods for behavioral experimentation and analysis in NHPs have noticeably failed to keep pace with these advances. As behavior ultimately lies at the junction between preclinical findings and its translation to clinical outcomes for brain disorders, approaches to improve the integrity, reproducibility, and translatability of behavioral experiments in NHPs requires critical evaluation. In this review, we provide a unifying account of existing brain disorder models using NHPs, and provide insights into the present and emerging contributions of behavioral studies to the field.

A hierarchical processing unit for multi-component behavior in the avian brain

Multi-component behavior is a form of goal-directed behavior that depends on the ability to execute various responses in a precise temporal order. Even though this function is vital for any species, little is known about how non-mammalian species accomplish such behavior and what the underlying neural mechanisms are. We show that humans and a non-mammalian species (pigeons) perform equally well in multi-component behavior and provide a validated experimental approach useful for cross-species comparisons. Applying molecular imaging methods, we identified brain regions most important for the examined behavioral dynamics in pigeons. Especially activity in the nidopallium intermedium medialis pars laterale (NIML) was specific to multi-component behavior since only activity in NIML was predictive for behavioral efficiency. The data suggest that NIML is important for hierarchical processing during goal-directed behavior and shares functional characteristics with the human inferior frontal gyrus in multi-component behavior.

•

Pigeons and humans perform equally well in the STOP-CHANGE paradigm

•

We identified relevant brain regions for the examined behavioral dynamics in pigeons

•

ZENK expression in NIML was predictive for behavioral efficiency

•

This study provides a validated experimental approach for cross-species comparisons

Consciousness without cortex

Sensory consciousness - the awareness and ability to report subjective experiences - is a property of biological nervous systems that has evolved out of unconscious processing over hundreds of millions of years. From which brain structures and based on which mechanisms can conscious experience emerge? Based on the body of work in human and nonhuman primates, the emergence of consciousness is intimately associated with the workings of the mammalian cerebral cortex with its specific cell types and layered structure. However, recent neurophysiological recordings demonstrate a neuronal correlate of consciousness in the pallial endbrain of crows. These telencephalic integration centers in birds originate embryonically from other pallial territories, lack a layered architecture characteristic for the cerebral cortex, and exhibit independently evolved pallial cell types. This argues that the mammalian cerebral cortex is not a prerequisite for consciousness to emerge in all vertebrates. Rather, it seems that the anatomical and physiological principles of the telencephalic pallium offer this structure as a brain substrate for consciousness to evolve independently across vertebrate phylogeny.

Pretecto- and ponto-cerebellar pathways to the pigeon oculomotor cerebellum follow a zonal organization

Both birds and mammals have relatively large forebrains and cerebella. In mammals, there are extensive sensory-motor projections to the cerebellum through the pontine nuclei originating from several parts of the cerebral cortex. Similar forebrain-to-cerebellum pathways exist in birds, but the organization of this circuitry has not been studied extensively. Birds have two nuclei at the base of the brainstem that are thought to be homologous to the pontine nuclei of mammals, the medial and lateral pontine nuclei (PM, PL). Additionally, birds are unique in that they have a pretectal nucleus called the medial spiriform nucleus (SpM) that, like the pontine nuclei, also receives projections from the forebrain and projects to the oculomotor cerebellum (OCb; folia VI to VIII). The OCb also receives input from the pretectal nucleus lentiformis mesencephali (LM), which analyzes visual optic flow information resulting from self-movement. In this study, we used single or double injections of fluorescent tracers to study the organization of these inputs from PM, PL, SpM and LM to the OCb in pigeons. We found that these inputs follow a zonal organization. The most medial zone in the OCb, zone A1, receives bilateral inputs from the lateral SpM, PL and LM. Zones A2 and C receive a bilateral projection from the medial SpM, and a mostly contralateral projection from PM and LM. We discuss how the pathway to zone A1 processes mainly visuo-motor information to spinal premotor areas, whereas the pathways to zone A2/C processes somato-motor and visuo-motor information and may have a feedback/modulatory role.

Working Memory: From Neural Activity to the Sentient Mind

Working memory (WM) is the ability to maintain and manipulate information in the conscious mind over a timescale of seconds. This ability is thought to be maintained through the persistent discharges of neurons in a network of brain areas centered on the prefrontal cortex, as evidenced by neurophysiological recordings in nonhuman primates, though both the localization and the neural basis of WM has been a matter of debate in recent years. Neural correlates of WM are evident in species other than primates, including rodents and corvids. A specialized network of excitatory and inhibitory neurons, aided by neuromodulatory influences of dopamine, is critical for the maintenance of neuronal activity. Limitations in WM capacity and duration, as well as its enhancement during development, can be attributed to properties of neural activity and circuits. Changes in these factors can be observed through training-induced improvements and in pathological impairments. WM thus provides a prototypical cognitive function whose properties can be tied to the spiking activity of brain neurons. © 2021 American Physiological Society. Compr Physiol 11:1-41, 2021.