Bounding the inefficiency of compromise

Social networks on the Internet have seen an enormous growth recently and play a crucial role in different aspects of today's life. They have facilitated information dissemination in ways that have been beneficial for their users but they are often used strategically in order to spread information that only serves the objectives of particular users. These properties have inspired a revision of classical opinion formation models from sociology using game-theoretic notions and tools. We follow the same modeling approach, focusing on scenarios where the opinion expressed by each user is a compromise between her internal belief and the opinions of a small number of neighbors among her social acquaintances. We formulate simple games that capture this behavior and quantify the inefficiency of equilibria using the well-known notion of the price of anarchy. Our results indicate that compromise comes at a cost that strongly depends on the neighborhood size

On Discrete Truthful Heterogeneous Two-Facility Location

We revisit the discrete heterogeneous two-facility location problem, in which there is a set of agents that occupy nodes of a line graph, and have private approval preferences over two facilities. When the facilities are located at some nodes of the line, each agent derives a cost that is equal to her total dis- tance from the facilities she approves. The goal is to decide where to locate the two facilities, so as to (a) incentivize the agents to truthfully report their preferences, and (b) achieve a good approximation of the minimum total (social) cost or the maximum cost among all agents. For both objectives, we de- sign deterministic strategyproof mechanisms with approximation ratios that significantly outperform the state-of-the-art, and complement these results with (almost) tight lower bounds

Bounding the Inefficiency of Compromise in Opinion Formation

Social networks on the Internet have seen an enormous growth recently and play a crucial role in different aspects of today’s life. They have facilitated information dissemination in ways that have been beneficial for their users but they are often used strategically in order to spread information that only serves the objectives of particular users. These properties have inspired a revision of classical opinion formation models from sociology using game-theoretic notions and tools. We follow the same modeling approach, focusing on scenarios where the opinion expressed by each user is a compromise between her internal belief and the opinions of a small number of neighbors among her social acquaintances. We formulate simple games that capture this behavior and quantify the inefficiency of equilibria using the well-known notion of the price of anarchy. Our results indicate that compromise comes at a cost that strongly depends on the neighborhood size

The Distortion of Distributed Facility Location

We study the distributed facility location problem, where a set of agents with positions on the line of real numbers are partitioned into disjoint districts, and the goal is to choose a point to satisfy certain criteria, such as optimize an objective function or avoid strategic behavior. A mechanism in our distributed setting works in two steps: For each district it chooses a point that is representative of the positions reported by the agents in the district, and then decides one of these representative points as the final output. We consider two classes of mechanisms: Unrestricted mechanisms which assume that the agents directly provide their true positions as input, and strategyproof mechanisms which deal with strategic agents and aim to incentivize them to truthfully report their positions. For both classes, we show tight bounds on the best possible approximation in terms of several minimization social objectives, including the well-known average social cost (average total distance of agents from the chosen point) and max cost (maximum distance among all agents from the chosen point), as well as other fairness-inspired objectives that are tailor-made for the distributed setting, in particular, the max-of-average and the average-of-max

Multi-Agent Systems for Computational Economics and Finance

In this article we survey the main research topics of our group at the University of Essex. Our research interests lie at the intersection of theoretical computer science, artificial intelligence, and economic theory. In particular, we focus on the design and analysis of mechanisms for systems involving multiple strategic agents, both from a theoretical and an applied perspective. We present an overview of our group’s activities, as well as its members, and then discuss in detail past, present, and future work in multi-agent systems

Aralar Sequesters GABA into Hyperactive Mitochondria, Causing Social Behavior Deficits

Social impairment is frequently associated with mitochondrial dysfunction and altered neurotransmission. Although mitochondrial function is crucial for brain homeostasis, it remains unknown whether mitochondrial disruption contributes to social behavioral deficits. Here, we show that Drosophila mutants in the homolog of the human CYFIP1, a gene linked to autism and schizophrenia, exhibit mitochondrial hyperactivity and altered group behavior. We identify the regulation of GABA availability by mitochondrial activity as a biologically relevant mechanism and demonstrate its contribution to social behavior. Specifically, increased mitochondrial activity causes gamma aminobutyric acid (GABA) sequestration in the mitochondria, reducing GABAergic signaling and resulting in social deficits. Pharmacological and genetic manipulation of mitochondrial activity or GABA signaling corrects the observed abnormalities. We identify Aralar as the mitochondrial transporter that sequesters GABA upon increased mitochondrial activity. This study increases our understanding of how mitochondria modulate neuronal homeostasis and social behavior under physiopathological conditions

Identification and Characterisation of Sodium Channel Nav1.7 Protein-Protein Interactions Using an Epitope-Tagged Gene-Targeted Mouse

Voltage-gated sodium channels are fundamental to the electrical properties of neurons. In mammals, ten isoforms of sodium channel are known and have been characterised (Nav1.1-1.9 and NaX). One particular subtype Nav1.7, plays a critical role in pain pathways and has a large number of functions including the control of neurotransmitter release, synaptic integration and the conduction of nociceptive signals. Humans born with loss of function mutations in this channel are unable to feel pain. This heritable disease known as congenital insensitivity to pain (CIP) can be recapitulated in transgenic mouse models and has made Nav1.7 a promising target for the development of analgesic drugs. However, this phenotype cannot be recapitulated with even the most specific of Nav1.7 channel blockers, possibly indicating that this channel’s role in pain signalling is more complex than simply signal transmission. In this thesis, we aimed to gain a greater understanding of Nav1.7 and its role in pain. Firstly, to further explore the function of this channel, we used an epitope-tagged Nav1.7 mouse that showed normal pain behaviour to identify and study the proteins that interact with this channel. The high-affinity epitope-tag consisted of a HAT-tag in tandem with a 3X FLAG tag separated by a Tobacco Etch Virus (TEV) cleavage site to enable two rounds of protein purification. Nav1.7 distribution throughout the central and peripheral nervous system was determined using Tap-tagged Nav1.7 mice. A Nav1.7 complex affinity-purified under native conditions by mass spectrometry revealed over 300 proteins associated with Nav1.7 in vivo, including previously known and novel interacting proteins. We conducted both validatory and functional assessments on these proteins. Previously known interactors included β-subunits as well as other signalling and synaptic proteins. We also showed an association with the Colapsin Response Mediator Protein 2 (CRMP2) and conducted a functional validation of this protein with regards to it’s trafficking role of Nav1.7. Furthermore, we identified this protein as one of the targets of the analgesic drug Lacosamide. We show that lacosamide acts through Nav1.7 in both a direct manner and through CRMP2 to reduce Nav1.7 channel current density. We also found and validated a number of synaptic proteins that interact with Nav1.7 such as Snap25 and synaptotagmin I and II. Moreover, we validated a number of interesting Nav1.7 interactions including L-type amino acid transporter 1 (Lat1), transmembrane P24 trafficking protein 10 (Tmed10), Neurofascin, A-kinase anchoring protein 12 (AKAP12) and G-protein regulated inducer of neurite outgrowth 1 (GPRIN1) (a µ-opioid receptor-binding protein), demonstrating a physical and functional link between Nav1.7 and opioid signalling. We further studied this link between Nav1.7 and opioid signalling. Type-A GPCRs are known to be regulated through a specific sodium binding site the occupancy of which diminishes agonist binding. We used an electrophysiological assay of Protein Kinase A activity to examine the role of intracellular sodium on opioid signalling. Phosphorylation of sodium channel Nav1.8 by activation of Protein Kinase A with db-cAMP is unaffected by altered intracellular sodium. By contrast, there is a dose-dependent inhibition of fentanyl action on Nav1.8 currents when intracellular sodium is increased from 0mM to 20mM. Fentanyl shows a 50% loss of activity and 80-fold increase in EC50 with 20mM intracellular sodium. These data suggest an effect of altered intracellular sodium levels on opioid receptors, where it might play a role in the modulation of opioid receptor signalling

Not All Strangers Are the Same: The Impact of Tolerance in Schelling Games

Schelling's famous model of segregation assumes agents of different types, who would like to be located in neighborhoods having at least a certain fraction of agents of the same type. We consider natural generalizations that allow for the possibility of agents being tolerant towards other agents, even if they are not of the same type. In particular, we consider an ordering of the types, and make the realistic assumption that the agents are in principle more tolerant towards agents of types that are closer to their own according to the ordering. Based on this, we study the strategic games induced when the agents aim to maximize their utility for a variety of tolerance levels. We provide a collection of results about the existence of equilibria, and their quality in terms of social welfare