Performance Baseline of Phase Transfer Entropy Methods for Detecting Animal Brain Area Interactions.

Objective: Phase transfer entropy (TEθ) methods perform well in animal sensory-spatial associative learning. However, their advantages and disadvantages remain unclear, constraining their usage. Method: This paper proposes the performance baseline of the TEθ methods. Specifically, four TEθ methods are applied to the simulated signals generated by a neural mass model and the actual neural data from ferrets with known interaction properties to investigate the accuracy, stability, and computational complexity of the TEθ methods in identifying the directional coupling. Then, the most suitable method is selected based on the performance baseline and used on the local field potential recorded from pigeons to detect the interaction between the hippocampus (Hp) and nidopallium caudolaterale (NCL) in visual-spatial associative learning. Results: (1) This paper obtains a performance baseline table that contains the most suitable method for different scenarios. (2) The TEθ method identifies an information flow preferentially from Hp to NCL of pigeons at the θ band (4-12 Hz) in visual-spatial associative learning. Significance: These outcomes provide a reference for the TEθ methods in detecting the interactions between brain areas.

Behavioral and Neuronal Representation of Numerosity Zero in the Crow.

Different species of animals can discriminate numerosity, the countable number of objects in a set. The representations of countable numerosities have been deciphered down to the level of single neurons. However, despite its importance for human number theory, a special numerical quantity, the empty set (numerosity zero), has remained largely unexplored. We explored the behavioral and neuronal representation of the empty set in carrion crows. Crows were trained to discriminate small numerosities including the empty set. Performance data showed a numerical distance effect for the empty set in one crow, suggesting that the empty set and countable numerosities are represented along the crows' "mental number line." Single-cell recordings in the endbrain region nidopallium caudolaterale (NCL) showed a considerable proportion of NCL neurons tuned to the preferred numerosity zero. As evidenced by neuronal distance and size effects, NCL neurons integrated the empty set in the neural number line. A subsequent neuronal population analysis using a statistical classifier approach showed that the neuronal numerical representations were predictive of the crows' success in the task. These behavioral and neuronal data suggests that the conception of the empty set as a cognitive precursor of a zero-like number concept is not an exclusive property of the cerebral cortex of primates. Zero as a quantitative category cannot only be implemented in the layered neocortex of primates, but also in the anatomically distinct endbrain circuitries of birds that evolved based on convergent evolution.SIGNIFICANCE STATEMENT The conception of "nothing" as number "zero" is celebrated as one of the greatest achievements in mathematics. To explore whether precursors of zero-like concepts can be found in vertebrates with a cerebrum that anatomically differs starkly from our primate brain, we investigated this in carrion crows. We show that crows can grasp the empty set as a null numerical quantity that is mentally represented next to number one. Moreover, we show that single neurons in an associative avian cerebral region specifically respond to the empty set and show the same physiological characteristics as for countable quantities. This suggests that zero as a quantitative category can also be implemented in the anatomically distinct endbrain circuitries of birds that evolved based on convergent evolution.

Avian nidopallium caudolaterale mediates decision-making during goal-directed navigation.

Previous work demonstrates that nidopallium caudolaterale, which is considered to be an analog of the mammalian prefrontal cortex, participates in goal-directed navigation in pigeons. However, its role remains unclear. To clarify its role, two goal-directed navigation tasks in plus-maze were designed, in which the goal location of one is random, and the other is fixed, i.e., the random-goal task and the fixed-goal task. The animals were trained to run from the starting location to the goal location in accordance with the cue in the plus-maze. The goal location is variable for the random-goal task but unchanged for the fixed-goal task. The results have demonstrated that the time point of nidopallium caudolaterale neuron response is consistent with decision-making. During the decision-making, the firing rates significantly increased in two tasks, which can also decode the direction of upcoming movement in the random-goal task. However, the location of decision-making is different between the tasks mentioned above. The decision-making window is at the intersection in the random-goal task, which is a departure in the fixed-goal task. In addition, these results also provide evidence that the neural activities obtained from the nidopallium caudolaterale may contain the decision-making information during goal-directed navigation. These results suggest that the avian nidopallium caudolaterale and the mammalian prefrontal cortex may play a similar role in goal-directed spatial decision-making. Additionally, these also may provide some support to understand the neural mechanism of decision-making for different species.

Neurons selective to the number of visual items in the corvid songbird endbrain.

It is unknown whether anatomical specializations in the endbrains of different vertebrates determine the neuronal code to represent numerical quantity. Therefore, we recorded single-neuron activity from the endbrain of crows trained to judge the number of items in displays. Many neurons were tuned for numerosities irrespective of the physical appearance of the items, and their activity correlated with performance outcome. Comparison of both behavioral and neuronal representations of numerosity revealed that the data are best described by a logarithmically compressed scaling of numerical information, as postulated by the Weber-Fechner law. The behavioral and neuronal numerosity representations in the crow reflect surprisingly well those found in the primate association cortex. This finding suggests that distantly related vertebrates with independently developed endbrains adopted similar neuronal solutions to process quantity.

Associative learning rapidly establishes neuronal representations of upcoming behavioral choices in crows.

The ability to form associations between behaviorally relevant sensory stimuli is fundamental for goal-directed behaviors. We investigated neuronal activity in the telencephalic area nidopallium caudolaterale (NCL) while two crows (Corvus corone) performed a delayed association task. Whereas some paired associates were familiar to the crows, novel associations had to be learned and mapped to the same target stimuli within a single session. We found neurons that prospectively encoded the chosen test item during the delay for both familiar and newly learned associations. These neurons increased their selectivity during learning in parallel with the crows' increased behavioral performance. Thus, sustained activity in the NCL actively processes information for the upcoming behavioral choice. These data provide new insights into memory representations of behaviorally meaningful stimuli in birds, and how such representations are formed during learning. The findings suggest that the NCL plays a role in learning arbitrary associations, a cornerstone of corvids' remarkable behavioral flexibility and adaptability.

[Measurement and performance analysis of functional neural network].

The measurement of network is one of the important researches in resolving neuronal population information processing mechanism using complex network theory. For the quantitative measurement problem of functional neural network, the relation between the measure indexes, i.e. the clustering coefficient, the global efficiency, the characteristic path length and the transitivity, and the network topology was analyzed. Then, the spike-based functional neural network was established and the simulation results showed that the measured network could represent the original neural connections among neurons. On the basis of the former work, the coding of functional neural network in nidopallium caudolaterale (NCL) about pigeon's motion behaviors was studied. We found that the NCL functional neural network effectively encoded the motion behaviors of the pigeon, and there were significant differences in four indexes among the left-turning, the forward and the right-turning. Overall, the establishment method of spike-based functional neural network is available and it is an effective tool to parse the brain information processing mechanism.

Neuronal correlates of visual working memory in the corvid endbrain.

The concept of working memory is key to cognitive functioning. Working memory encompasses the capacity to retain immediately past information, to process this information, and to use it to guide goal-directed behavior. Corvid songbirds are renowned for their high-level cognitive capabilities, but where and how visual information is temporarily retained by neurons in the avian brain in a behaviorally relevant way remains poorly understood. We trained four carrion crows (Corvus corone) on versions of a delayed match-to-sample task that required the crows to remember a visual stimulus for later comparison. While the crows performed the task, we recorded the activity of single neurons in the nidopallium caudolaterale (NCL), a pallial association area of the avian endbrain. We show that many NCL neurons encode information about visual stimuli and temporarily maintain this information after the stimulus disappeared by sustained delay activity. Selective delay activity allows the birds to hold relevant information in memory and correlates with discrimination behavior. This suggests that sustained activity of NCL neurons is a neuronal correlate of visual working memory in the corvid brain and serves to bridge temporal gaps, thereby offering a workspace for processing immediately past visual information.

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.

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.

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.

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.

"Prefrontal" Neuronal Foundations of Visual Asymmetries in Pigeons.

This study was conducted in order to reveal the possibly lateralized processes in the avian nidopallium caudolaterale (NCL), a functional analogue to the mammalian prefrontal cortex, during a color discrimination task. Pigeons are known to be visually lateralized with a superiority of the left hemisphere/right eye for visual feature discriminations. While animals were working on a color discrimination task, we recorded single visuomotor neurons in left and right NCL. As expected, pigeons learned faster and responded more quickly when seeing the stimuli with their right eyes. Our electrophysiological recordings discovered several neuronal properties of NCL neurons that possibly contributed to this behavioral asymmetry. We found that the speed of stimulus encoding was identical between left and right NCL but action generation was different. Here, most left hemispheric NCL neurons reached their peak activities shortly before response execution. In contrast, the majority of right hemispheric neurons lagged behind and came too late to control the response. Thus, the left NCL dominated the animals' behavior not by a higher efficacy of encoding, but by being faster in monopolizing the operant response. A further asymmetry concerned the hemisphere-specific integration of input from the contra- and ipsilateral eye. The left NCL was able to integrate and process visual input from the ipsilateral eye to a higher degree and thus achieved a more bilateral representation of two visual fields. We combine these novel findings with those from previous publications to come up with a working hypothesis that could explain how hemispheric asymmetries for visual feature discrimination in birds are realized by a sequential buildup of lateralized neuronal response properties in the avian forebrain.

Elevated Gamma Connectivity in Nidopallium Caudolaterale of Pigeons during Spatial Path Adjustment.

Previous studies showed that spatial navigation depends on a local network including multiple brain regions with strong interactions. However, it is still not fully understood whether and how the neural patterns in avian nidopallium caudolaterale (NCL), which is suggested to play a key role in navigation as a higher cognitive structure, are modulated by the behaviors during spatial navigation, especially involved path adjustment needs. Hence, we examined neural activity in the NCL of pigeons and explored the local field potentials' (LFPs) spectral and functional connectivity patterns in a goal-directed spatial cognitive task with the detour paradigm. We found the pigeons progressively learned to solve the path adjustment task when the learned path was blocked suddenly. Importantly, the behavioral changes during the adjustment were accompanied by the modifications in neural patterns in the NCL. Specifically, the spectral power in lower bands (1-4 Hz and 5-12 Hz) decreased as the pigeons were tested during the adjustment. Meanwhile, an elevated gamma (31-45 Hz and 55-80 Hz) connectivity in the NCL was also detected. These results and the partial least square discriminant analysis (PLS-DA) modeling analysis provide insights into the neural activities in the avian NCL during the spatial path adjustment, contributing to understanding the potential mechanism of avian spatial encoding. This study suggests the important role of the NCL in spatial learning, especially path adjustment in avian navigation.

Enhanced Hippocampus-Nidopallium Caudolaterale Connectivity during Route Formation in Goal-Directed Spatial Learning of Pigeons.

Goal-directed spatial learning is crucial for the survival of animals, in which the formation of the route from the current location to the goal is one of the central problems. A distributed brain network comprising the hippocampus and prefrontal cortex has been shown to support such capacity, yet it is not fully understood how the most similar brain regions in birds, the hippocampus (Hp) and nidopallium caudolaterale (NCL), cooperate during route formation in goal-directed spatial learning. Hence, we examined neural activity in the Hp-NCL network of pigeons and explored the connectivity dynamics during route formation in a goal-directed spatial task. We found that behavioral changes in spatial learning during route formation are accompanied by modifications in neural patterns in the Hp-NCL network. Specifically, as pigeons learned to solve the task, the spectral power in both regions gradually decreased. Meanwhile, elevated hippocampal theta (5 to 12 Hz) connectivity and depressed connectivity in NCL were also observed. Lastly, the interregional functional connectivity was found to increase with learning, specifically in the theta frequency band during route formation. These results provide insight into the dynamics of the Hp-NCL network during spatial learning, serving to reveal the potential mechanism of avian spatial navigation.

Hippocampus-nidopallium caudolaterale interactions exist in the goal-directed behavior of pigeon.

Avian hippocampus (Hp) and nidopallium caudolaterale (NCL) are believed to play key roles in goal-directed behavior. However, it is still unclear whether there are interactions between the two brain regions in the goal-directed behavior of pigeons. To investigate the interactions between the Hp and the NCL in the goal-directed behavior, we recorded local field potential (LFP) signals from the two regions simultaneously when the pigeons performed a goal-directed decision-making task. Amplitude-amplitude coupling analysis revealed that the coupling value between the LFP recorded from the Hp and that from the NCL increased significantly (P < 0.05) in slow gamma-band (40-60 Hz) during the turning area. In addition, the LFP functional network analysis demonstrated the LFP functional connections between the Hp and the NCL increased significantly (P < 0.05) in the turning area. The result of partial directed coherence (PDC) analysis showed that the predominant direction of information flow is thought to be from the Hp to the NCL. These findings suggest that there are causal functional interactions between the Hp and the NCL by which information is transmitted between the two regions relevant to goal-directed behavior.

Neuronal Correlates of Spatial Working Memory in the Endbrain of Crows.

Birds are renowned for their excellent spatial cognition. Corvid songbirds, in particular, rely on explicit representation of spatial cues in memory when caching food and retrieving caches for later consumption. However, the neuronal correlates of flexible spatial memory abilities are largely unknown in birds. We therefore trained carrion crows (Corvus corone) on a spatial delayed-response task in which they had to maintain the variable location of a visual item for a few seconds in working memory. After the crows performed this task with high precision, we recorded single-cell activity from the associative endbrain area Nidopallium caudolaterale (NCL) in the behaving crows. A large fraction of NCL neurons were tuned to individual preferred locations and selectively maintained the spatial location of items in working memory. A comparison of firing rates with reaction times suggested that the majority of delay-selective neurons represented stored location information rather than motor preparation. Almost 30% of all recorded neurons were tuned during both visual presentation and memory delay, and their spatial tuning was significantly correlated. The population of recorded neurons stably maintained spatial information over the course of the working memory period. Importantly, the neural responses of spatially tuned neurons were relevant for the crows' choices and allowed a statistical classifier to predict the subsequently chosen target location in free-choice trials. Our findings demonstrate the pivotal role of the avian NCL in spatial working memory that is reminiscent of the function of the convergently evolved primate prefrontal cortex in spatial working memory.

Goal-directed behavior elevates gamma oscillations in nidopallium caudolaterale of pigeon.

Avian nidopallium caudolaterale (NCL), a functional analogue of mammalian prefrontal cortex, is thought to be participated to goal-directed behavior. However, few studies so far investigated local field potential (LFP) properties within this area. In this study, we recorded the LFP activity from the NCL of six pigeons when they performed a goal-directed decision-making task in a plus-maze. Spectral analysis revealed a significant LFP-power increase in the gamma-band (40-60Hz) during the decision-making process. Moreover, the LFP activity in the gamma-band was modulated by the behavioral outcomes of pigeons. It could decode effectively the motion directions of animals. These results indicate that the gamma rhythm of LFP recorded from the NCL correlates with the goal-directed behavior of pigeons.

Exploring the Relationship between Brain Plasticity, Migratory Lifestyle, and Social Structure in Birds.

Studies in Passerines have found that migrating species recruit more new neurons into brain regions that process spatial information, compared with resident species. This was explained by the greater exposure of migrants to spatial information, indicating that this phenomenon enables enhanced navigational abilities. The aim of the current study was to test this hypothesis in another order-the Columbiformes - using two closely-related dove species-the migrant turtle-dove (Streptopelia turtur) and the resident laughing dove (S. senegalensis), during spring, summer, and autumn. Wild birds were caught, treated with BrdU, and sacrificed 5 weeks later. New neurons were recorded in the hyperpallium apicale, hippocampus and nidopallium caudolaterale regions. We found that in doves, unlike passerines, neuronal recruitment was lower in brains of the migratory species compared with the resident one. This might be due to the high sociality of doves, which forage and migrate in flocks, and therefore can rely on communal spatial knowledge that might enable a reduction in individual navigation efforts. This, in turn, might enable reduced levels of neuronal recruitment. Additionally, we found that unlike in passerines, seasonality does not affect neuronal recruitment in doves. This might be due to their non-territorial and explorative behavior, which exposes them to substantial spatial information all year round. Finally, we discuss the differences in neuronal recruitment between Columbiformes and Passeriformes and their possible evolutionary explanations. Our study emphasizes the need to further investigate this phenomenon in other avian orders and in additional species.

The role of nidopallium caudolaterale in the goal-directed behavior of pigeons.

Avian nidopallium caudolaterale (NCL) is believed to be analogue to the mammalian prefrontal cortex (PFC), a key brain region for guiding goal-directed behavior. But the role of NCL during goal-directed behavior remains unclear. To investigate whether the pigeon NCL participate in the goal-directed behavior, we recorded single-units from the NCL of four pigeons as they performing goal-directed decision-making task in a plus-maze. During the decision-making process, the firing rates of NCL neurons significantly increased and they are associated with the choice of the upcoming movement. Moreover, both the firing rates and the decoding performance in the correct trials are significantly higher both of that in the error trials. These suggest that the NCL neurons indeed participate in the goal-directed behavior of pigeon and the neural activities may be induced by the rewards. However, the NCL neurons are depend on the rewards received to produce firing patterns discriminating the features of goal-directed behaviors, rather than encode the reward itself. In addition, we found that the functional components of goal-directed behavior are lateralized in the NCL, both the firing rates and the decoding performance in left NCL are significantly higher than both of that in right NCL.