No abstract

Borrowing and lending between sovereign parties is modelled as intertemporal barter that smooths the consumption of a risk-averse party subject to endowment shocks. The surplus anticipated in the relationship offers sufficient incentive for cooperation by all parties, including any other competitive lenders who may be potential entrants. The sole punishments consist of renegotiation-proof changes in the paths of future payments. This implicit long-term relationship may be fulfilled as the continual renegotiation of a simple, incomplete short-term debt contract with associated "debt overhang." The analysis suggests that the crucial role of the explicit contract is the identification of the parties to the relationship.

Song is a learned vocal behavior influenced by social interactions. Prior work has suggested that the anterior forebrain pathway (AFP), a specialized pallial-basal ganglia circuit critical for vocal plasticity, mediates the influence of social signals on song. Here, we investigate the signals the AFP sends to song motor areas and their dependence on social context by characterizing singing-related activity of single neurons in the AFP output nucleus LMAN (lateral magnocellular nucleus of the anterior nidopallium). We show that interaction with females causes marked, real-time changes in firing properties of individual LMAN neurons. When males sing to females ("directed"), LMAN neurons exhibit reliable firing of single spikes precisely locked to song. In contrast, when males sing alone ("undirected"), the same LMAN neurons exhibit prominent burst firing and trial-by-trial variability. Burst structure and timing vary substantially across repeated undirected trials. Despite context-dependent differences in firing statistics, the average pattern of song-locked firing for an individual neuron is similar across behavioral contexts, suggesting a common underlying signal. Different LMAN neurons in the same bird, however, exhibit distinct firing patterns, suggesting that subsets of neurons jointly encode song features. Together, our findings demonstrate that behavioral interactions reversibly transform the signaling mode of LMAN neurons. Such changes may contribute to rapid switching of motor activity between variable and precise states. More generally, our results suggest that pallial-basal ganglia circuits contribute to motor learning and production through multiple mechanisms: patterned signals could guide changes in motor output while state-dependent variability could subserve motor exploration.

Recent volatility of prices of major grains has generated a wide array of analyses and policy prescriptions that reveal the inability of economists to approach a consensus on the nature of the phenomenon and its implications for policy. This review of market events and their economic interpretations finds that recent price spikes are not as unusual as many discussions imply. Further, the balance between consumption, available supply, and stocks seems to be as relevant for our understanding of these markets as it was decades ago. Though there is much to be learned about commodity markets, the tools at hand are capable of explaining the main forces at work, and of giving good guidance to policymakers confronted with a bewildering variety of expensive policy prescriptions.