The pure Nash equilibrium property and the quasi-acyclic condition

This paper presents a sufficient condition for the quasi-acyclic condition. A game is quasi-acyclic if from any strategy profile, there exists a finite sequence of strict best replies that ends in a pure strategy Nash equilibrium. The best-reply dynamics must converge to a pure strategy Nash equilibrium in any quasi-acyclic game. A game has the pure Nash equilibrium property (PNEP) if there is a pure strategy Nash equilibrium in any game constructed by restricting the set of strategies to a subset of the set of strategies in the original game. Any finite, ordinal potential game and any finite, supermodular game have the PNEP. We show that any finite, two-player game with the PNEP is quasi-acyclic.best-reply dynamics

Evolution of competitive equilibrium with endogenous product differentiation

Previous theoretical researches show that learning from good performers yields intense competition and results in the low profitability of firms. These researchers do not take into account differentiation strategies being referred as a useful strategic tool to mitigate competition. We introduce an evolutionary (learning) game into a duopoly model with product differentiation on the Hotelling line. We find that central agglomeration appears in the unique stochastically stable state in which the equilibrium price is equal to the marginal cost of firms. This implies that perfectly competitive equilibrium appears even when firms have an opportunity to differentiate themselves through product differentiation and to mitigate competition.

"Voice Matters in a Dictator Game"

We examine a dictator game with a "voice" option in the laboratory. In our experiment, the recipient has an opportunity to state a payoff-irrelevant request for the minimum acceptable offer before the dictator dictates his/her offer. In this game, it is predicted not only by the standard game theory, but by the behavioral game theory such as theories of other-regarding preferences, that the dictator's offer is independent of the recipient's request. Some findings based on our data are as follows: the above independence hypothesis is rejected; as the recipient's request increases, the dictator's offer increases when the requests are less than 50% of the pie; on the other hand, when the request goes beyond 50% of the pie, the offer decreases as the request increases. That is, "voice" matters in a dictator game. We also conduct a clustering analysis to classify dictators' behaviour into some notable patterns. As a result, we obtain the following three behavioural patterns: the other-disregarding, the punishing the greedy, and the lenient.

mRNA expression profile of serotonin receptor subtypes and distribution of serotonergic terminations in marmoset brain

To better understand serotonin function in the primate brain, we examined the mRNA expression patterns of all the 13 members of the serotonin receptor (5HTR) family, by in situ hybridization and the distribution of serotonergic terminations by serotonin transporter (SERT) protein immunohistochemical analysis. Ten of the 13 5HTRs showed significant mRNA expressions in the marmoset brain. Our study shows several new features of the organization of serotonergic systems in the marmoset brain. (1) The thalamus expressed only a limited number of receptor subtypes compared with the cortex, hippocampus, and other subcortical regions. (2) In the cortex, there are layer-selective and area-selective mRNA expressions of 5HTRs. (3) Highly localized mRNA expressions of 5HT1F and 5HT3A were observed. (4) There was a conspicuous overlap of the mRNA expressions of receptor subtypes known to have somatodendritic localization of receptor proteins with dense serotonergic terminations in the visual cortex, the central lateral nucleus of the thalamus, the presubiculum, and the medial mammillary nucleus of the hypothalamus. This suggests a high correlation between serotonin availability and receptor expression at these locations. (5) The 5HTRs show differences in mRNA expression pattern between the marmoset and mouse cortices whereas the patterns of both the species were much similar in the hippocampus. We discuss the possible roles of 5HTRs in the marmoset brain revealed by the analysis of their overall mRNA expression patterns

Cortical neural dynamics unveil the rhythm of natural visual behavior in marmosets

Numerous studies have shown that the visual system consists of functionally distinct ventral and dorsal streams; however, its exact spatial-temporal dynamics during natural visual behavior remain to be investigated. Here, we report cerebral neural dynamics during active visual exploration recorded by an electrocorticographic array covering the entire lateral surface of the marmoset cortex. We found that the dorsal stream was activated before the primary visual cortex with saccades and followed by the alteration of suppression and activation signals along the ventral stream. Similarly, the signal that propagated from the dorsal to ventral visual areas was accompanied by a travelling wave of low frequency oscillations. Such signal dynamics occurred at an average of 220 ms after saccades, which corresponded to the timing when whole-brain activation returned to background levels. We also demonstrated that saccades could occur at any point of signal flow, indicating the parallel computation of motor commands. Overall, this study reveals the neural dynamics of active vision, which are efficiently linked to the natural rhythms of visual exploration

"Voice Matters in a Dictator Game"(in Japanese)

We examine a dictator game with a "voice" option in the laboratory. In the dictator game, player 1 dictates how to divide a pie, and player 2 simply receives his/her share, i.e., unlike in an ultimatum game, he/she does not have an option to reject this division. In our experiment, player 2 has an opportunity to state a payoff-irrelevant request for the minimum acceptable offer before player 1 dictates his/her offer. In this game,it is predicted not only by the standard game theory, but by the behavioral game theory such as the theory of other-regarding preferences, that player 1's offer is independent of player 2's request. Some findings based on our data are as follows: the above independence hypothesis is rejected; as player 2's request increases, player 1's offer increases when the requests are less than 50% of the pie; on the other hand, when the request goes beyond 50% of the pie, the offer decreases as the request increases. That is, "voice" matters without having strategic meaning. We also conduct a clustering analysis to find three notably different tendencies among player 1's behavior.