Decision-making neural circuits mediating social behaviors

We propose a mathematical model of a continuous attractor network that controls social behaviors. The model is examined with bifurcation analysis and computer simulations. The results show that the model exhibits stable steady states and thresholds for steady state transitions corresponding to some experimentally observed behaviors, such as aggression control. The performance of the model and the relation with experimental evidence are discussed.     

Neural circuits and activity dynamics underlying sex-specific effects of chronic social isolation stress

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Innate synchronous oscillations in freely-organized small neuronal circuits

Background

Information processing in neuronal networks relies on the network''s ability to generate temporal patterns of action potentials. Although the nature of neuronal network activity has been intensively investigated in the past several decades at the individual neuron level, the underlying principles of the collective network activity, such as the synchronization and coordination between neurons, are largely unknown. Here we focus on isolated neuronal clusters in culture and address the following simple, yet fundamental questions: What is the minimal number of cells needed to exhibit collective dynamics? What are the internal temporal characteristics of such dynamics and how do the temporal features of network activity alternate upon crossover from minimal networks to large networks?

Methodology/Principal Findings

We used network engineering techniques to induce self-organization of cultured networks into neuronal clusters of different sizes. We found that small clusters made of as few as 40 cells already exhibit spontaneous collective events characterized by innate synchronous network oscillations in the range of 25 to 100 Hz. The oscillation frequency of each network appeared to be independent of cluster size. The duration and rate of the network events scale with cluster size but converge to that of large uniform networks. Finally, the investigation of two coupled clusters revealed clear activity propagation with master/slave asymmetry.

Conclusions/Significance

The nature of the activity patterns observed in small networks, namely the consistent emergence of similar activity across networks of different size and morphology, suggests that neuronal clusters self-regulate their activity to sustain network bursts with internal oscillatory features. We therefore suggest that clusters of as few as tens of cells can serve as a minimal but sufficient functional network, capable of sustaining oscillatory activity. Interestingly, the frequencies of these oscillations are similar those observed in vivo.     

Modulation of circuits underlying rhythmic behaviors

Summary What have we learned about behavior from neuromodulatory studies of the crustacean stomatogastric system? The emphasis of this paper has been on the analysis of one single class of behaviors (rhythmic) in terms of microcircuitry (synaptic connections between identified neurons). But in the general case, all behaviors result from the generation of spatio-temporal patterns by the central nervous system. How individual nerve cells interact with each other to produce such patterns is of fundamental interest. We know from work on simple networks that it is possible to link the circuitry of the nervous system with behavior in a precise way, and that instead of a large number of dedicated circuits, behaviors can be altered by chemically adjusting the functional properties of the neuronal elements. One circuit can be configured to perform a variety of different behaviors by activating neurons which contain neuromodulatory substances or in response to neurohormones circulating in the hemolymph. At present we know only a few of the ways neuromodulatory neurons are triggered to release their contents onto the neurons making up CPGs.The findings described here raise many questions. What are the parameters which control the distribution of neuromodulatory substances throughout the nervous system? What happens when more than one neuromodulator is present? At the cellular level, what mechanisms are involved in transforming each neuron from one functional state to another, and then how does the entire constellation of changes give rise to a new output? It is important to answer such questions in reduced networks, because there are presently no techniques available to answer them in the more complex networks of the brain. While there is no question that modulatory activity occurs in the brain, whether or not the principles which have been discovered by using simple invertebrate circuits scale up to vertebrate circuits remains an intriguing question.     

The social network: Neural control of sex differences in reproductive behaviors,motivation, and response to social isolation

Social animal species present a vast repertoire of social interactions when encountering conspecifics. Reproduction-related behaviors, such as mating, parental care, and aggression, are some of the most rewarding types of social interactions and are also the most sexually dimorphic ones. This review focuses on rodent species and summarizes recent advances in neuroscience research that link sexually dimorphic reproductive behaviors to sexual dimorphism in their underlying neuronal circuits. Specifically, we present a few possible mechanisms governing sexually-dimorphic behaviors, by hypothalamic and reward-related brain regions. Sex differences in the neural response to social isolation in adulthood are also discussed, as well as future directions for comparative studies with naturally solitary species.     

Social circuits: peptidergic regulation of mammalian social behavior

Mammals have developed patterns of social relationships that enhance the survival of individuals and maximize the reproductive success of species. Although social stimuli and social responses are highly complex, recent studies are providing substantial insights into their neural substrates. Neural pathways employing the nonapeptides vasopressin and oxytocin play a particularly prominent role both in social recognition and the expression of appropriate social responses. New insights into social neuroscience are discussed, along with the relevance of this rapidly developing field to human relationships and disease processes.     

Neural induction: old problem, new findings, yet more questions

During neural induction, the embryonic neural plate is specified and set aside from other parts of the ectoderm. A popular molecular explanation is the 'default model' of neural induction, which proposes that ectodermal cells give rise to neural plate if they receive no signals at all, while BMP activity directs them to become epidermis. However, neural induction now appears to be more complex than once thought, and can no longer be fully explained by the default model alone. This review summarizes neural induction events in different species and highlights some unanswered questions about this important developmental process.     

How MAP kinase modules function as robust,yet adaptable,circuits

Genetic and biochemical studies have revealed that the diversity of cell types and developmental patterns evident within the animal kingdom is generated by a handful of conserved, core modules. Core biological modules must be robust, able to maintain functionality despite perturbations, and yet sufficiently adaptable for random mutations to generate phenotypic variation during evolution. Understanding how robust, adaptable modules have influenced the evolution of eukaryotes will inform both evolutionary and synthetic biology. One such system is the MAP kinase module, which consists of a 3-tiered kinase circuit configuration that has been evolutionarily conserved from yeast to man. MAP kinase signal transduction pathways are used across eukaryotic phyla to drive biological functions that are crucial for life. Here we ask the fundamental question, why do MAPK modules follow a conserved 3-tiered topology rather than some other number? Using computational simulations, we identify a fundamental 2-tiered circuit topology that can be readily reconfigured by feedback loops and scaffolds to generate diverse signal outputs. When this 2-kinase circuit is connected to proximal input kinases, a 3-tiered modular configuration is created that is both robust and adaptable, providing a biological circuit that can regulate multiple phenotypes and maintain functionality in an uncertain world. We propose that the 3-tiered signal transduction module has been conserved through positive selection, because it facilitated the generation of phenotypic variation during eukaryotic evolution.     

Neural circuits for jumping in the locust

The locust jump consists of three distinct phases: Cocking: a rapid flexion of both hindleg tibia and locking of both tibia in full flexion. Co-contraction: simultaneous contractions in hindleg flexor and extensor muscles lasting about 0.5 s resulting in the storage of energy for the jump in elastic elements of the legs and muscles. Triggering: a sudden inhibition of flexor activity to allow the shortening of the contracted extensors and the release of the energy stored during the co-contraction phase. The neural circuitry controlling these three phases is now reasonably well understood. Some of its major features are: (1) pairs of large identifiable interneurons in the thoracic ganglia for evoking the cocking response (C-neurons) and for triggering the jump (M-neurons), (2) a central excitatory pathway from extensor to flexor tibiae motoneurons to ensure simultaneous activation of extensor and flexor motoneurons during the initial part of the co-contraction phase, (3) a positive feedback pathway from cuticular receptors to extensor motoneurons for maintaining extensor activity during the co-contraction phase, (4) proprioceptive feedback to the trigger interneurons for increasing their excitability during the co-contraction phase and thereby allowing a variety of external stimuli to activate the trigger neurons and evoke a jump, (5) presynaptic inhibition of visual pathways to the trigger neurons to ensure that the trigger neurons are not activated by the simultaneous occurrence of visual and auditory stimuli in the absence of proprioceptive input, and (6) a pair of multifunctional visual movement detecting neurons which can initiate cocking or trigger the jump depending on the animal's state.