The canonical circuit of the avian forebrain

Die vorliegende Arbeit ist eine anatomische Untersuchung der lokalen neuronalen Schaltkreise des Vogelgehirns. Untersucht wurden der Hippocampus, das Hyperpallium und die trigeminalen, visuellen und auditorischen Areale im Vorderhirn. Die Ergebnisse haben gezeigt, dass der Hippocampus ein komplexes rekurrentes Verschaltungsmuster aufweist. Die Verbindungen folgten einer strikten topografischen Anordnung entlang der transversalen Axis des Hippocampus. Weiterhin konnte gezeigt werden, dass die lokale Verschaltung in den sensorischen Arealen des Vorderhirns erstaunliche Ähnlichkeiten zu dem Neocortex der Säugetiere aufweist. Trotz früheren Annahmen scheint das Vogelgehirn eine schichten- und säulen-artige Organisation zu besitzen. Diese Arbeit liefert einen wichtigen Beitrag zu den evolutionären Theorien der komparativen Neurobiologie und stellt eine anatomische Basis für die Erforschung der neuronalen Mechanismen des Verhaltens auf der Schaltkreisebene in weiteren Studien

Constraint satisfaction with counting quantifiers

We initiate the study of constraint satisfaction problems (CSPs) in the presence of counting quantifiers, which may be seen as variants of CSPs in the mould of quantified CSPs (QCSPs). We show that a single counting quantifier strictly between exists^1:=exists and exists^n:=forall (the domain being of size n) already affords the maximal possible complexity of QCSPs (which have both exists and forall), being Pspace-complete for a suitably chosen template. Next, we focus on the complexity of subsets of counting quantifiers on clique and cycle templates. For cycles we give a full trichotomy -- all such problems are in L, NP-complete or Pspace-complete. For cliques we come close to a similar trichotomy, but one case remains outstanding. Afterwards, we consider the generalisation of CSPs in which we augment the extant quantifier exists^1:=exists with the quantifier exists^j (j not 1). Such a CSP is already NP-hard on non-bipartite graph templates. We explore the situation of this generalised CSP on bipartite templates, giving various conditions for both tractability and hardness -- culminating in a classification theorem for general graphs. Finally, we use counting quantifiers to solve the complexity of a concrete QCSP whose complexity was previously open

Constraint Satisfaction with Counting Quantifiers

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Mechanistic flexibility of the retrosplenial cortex enables its contribution to spatial cognition

The retrosplenial cortex (RC) is a brain structure crucial for spatial navigation and memory. It contains neurons such as $\underline{head}$ $\underline{direction}$ $\underline{cells}$, border cells, as well as other cells supporting spatial and contextual encoding. How such complex and diverse neuronal properties are generated by RC microcircuitry and how they jointly orchestrate subsequent behavior remains enigmatic. Here, we consider recent findings that extend current knowledge about how the RC modulates spatial navigation and spatial cognition. We argue that the integrative properties of RC allow the combination of idiothetic cues, spatial relations (allocentric and egocentric), and environmental features (landmarks, boundaries, etc.) into a spatial map that can dynamically support goal-directed navigation. Furthermore, the mnemonic functions of RC suggest its possible role in autobiographical information storage

The intriguing contribution of hippocampal long-term depression to spatial learning and long-term memory

Long-term potentiation (LTP) and long-term depression (LTD) comprise the principal cellular mechanisms that fulfill established criteria for the physiological correlates of learning and memory. Traditionally LTP, that increases synaptic weights, has been ascribed a prominent role in learning and memory whereas LTD, that decreases them, has often been relegated to the category of "counterpart to LTP" that serves to prevent saturation of synapses. In contradiction of these assumptions, studies over the last several years have provided functional evidence for distinct roles of LTD in specific aspects of hippocampus-dependent associative learning and information encoding. Furthermore, evidence of the experience-dependent "pruning" of excitatory synapses, the majority of which are located on dendritic spines, by means of LTD has been provided. In addition, reports exist of the temporal and physical restriction of LTP in dendritic compartments by means of LTD. Here, we discuss the role of LTD and LTP in experience-dependent information encoding based on empirical evidence derived from conjoint behavioral and electrophysiological studies conducted in behaving rodents. We pinpoint the close interrelation between structural modifications of dendritic spines and the occurrence of LTP and LTD. We report on findings that support that whereas LTP serves to acquire the general scheme of a spatial representation, LTD enables retention of content details. We argue that LTD contributes to learning by engaging in a functional interplay with LTP, rather than serving as its simple counterpart, or negator. We propose that similar spatial experiences that share elements of neuronal representations can be modified by means of LTD to enable pattern separation. Therewith, LTD plays a crucial role in the disambiguation of similar spatial representations and the prevention of generalization

Functional connectivity pattern of the internal hippocampal network in awake pigeons

In the last two decades, the avian hippocampus has been repeatedly studied with respect to its architecture, neurochemistry, and connectivity pattern. We review these insights and conclude that we unfortunately still lack proper knowledge on the interaction between the different hippocampal subregions. To fill this gap, we need information on the functional connectivity pattern of the hippocampal network. These data could complement our structural connectivity knowledge. To this end, we conducted a resting-state fMRI experiment in awake pigeons in a 7-T MR scanner. A voxel-wise regression analysis of blood oxygenation leveldependent (BOLD) fluctuations was performed in 6 distinct areas, dorsomedial (DM), dorsolateral (DL), triangular shaped (Tr), dorsolateral corticoid (CDL), temporo-parieto-occipital (TPO), and lateral septum regions (SL), to establish a functional connectivity map of the avian hippocampal network. Our study reveals that the system of connectivities between CDL, DL, DM, and Tr is the functional backbone of the pigeon hippocampal system. Within this network, DM is the central hub and is strongly associated with DL and CDL BOLD signal fluctuations. DM is also the only hippocampal region to which large Tr areas are functionally connected. In contrast to published tracing data, TPO and SL are only weakly integrated in this network. In summary, our findings uncovered a structurally otherwise invisible architecture of the avian hippocampal formation by revealing the dynamic blueprints of this network

A three-dimensional digital atlas of the starling brain

International audienceBecause of their sophisticated vocal behaviour, their social nature, their high plasticity and their robustness, starlings have become an important model species that is widely used in studies of neuroethology of song production and perception. Since Magnetic Resonance Imaging (MRI) represents an increasingly relevant tool for comparative neuroscience, a 3-dimensional MRI-based atlas of the starling brain becomes essential. Using multiple imaging protocols we delineated several sensory systems as well as the song control system. This starling brain atlas can easily be used to determine the stereotactic location of identified neural structures at any angle of the head. Additionally, the atlas is useful to find the optimal angle of sectioning for slice experiments, stereotactic injections and electrophysiological recordings. The starling brain atlas is freely available for the scientific community