Does bounded rationality lead to individual heterogeneity? The impact of the experimentation process and of memory constraints

In this paper we explore the effect of bounded rationality on the convergence of individual behavior toward equilibrium. In the context of a Cournot game with a unique and symmetric Nash equilibrium, firms are modeled as adaptive economic agents through a genetic algorithm. Computational experiments show that (1) there is remarkable heterogeneity across identical but boundedly rational agents; (2) such individual heterogeneity is not simply a consequence of the random elements contained in the genetic algorithm; (3) the more rational agents are in terms of memory abilities and pre-play evaluation of strategies, the less heterogeneous they are in their actions. At the limit case of full rationality, the outcome converges to the standard result of uniform individual behavior.

Memory in contracts: the experience of the EBRD (1991-2003)

The objective of this paper is to identify the role of memory in repeated contracts with moral hazard in financial intermediation. We use the database we have built containing the contracts signed by the European Bank for Reconstruction and Development EBRD between 1991 and 2003. Our framework is a standard setting of repeated moral hazard. After having controlled for the adverse selection component, we are able to prove that client reputation is the discrimination device according to which the bank fixes the amount of credit for the established clients. Our results unambiguously isolate the effect of memory in the bank's lending decisions.

Constitutive activation of Wnt signaling favors generation of memory CD8 T cells.

T cell factor-1 (TCF-1) and lymphoid enhancer-binding factor 1, the effector transcription factors of the canonical Wnt pathway, are known to be critical for normal thymocyte development. However, it is largely unknown if it has a role in regulating mature T cell activation and T cell-mediated immune responses. In this study, we demonstrate that, like IL-7Ralpha and CD62L, TCF-1 and lymphoid enhancer-binding factor 1 exhibit dynamic expression changes during T cell responses, being highly expressed in naive T cells, downregulated in effector T cells, and upregulated again in memory T cells. Enforced expression of a p45 TCF-1 isoform limited the expansion of Ag-specific CD8 T cells in response to Listeria monocytogenes infection. However, when the p45 transgene was coupled with ectopic expression of stabilized beta-catenin, more Ag-specific memory CD8 T cells were generated, with enhanced ability to produce IL-2. Moreover, these memory CD8 T cells expanded to a larger number of secondary effectors and cleared bacteria faster when the immunized mice were rechallenged with virulent L. monocytogenes. Furthermore, in response to vaccinia virus or lymphocytic choriomeningitis virus infection, more Ag-specific memory CD8 T cells were generated in the presence of p45 and stabilized beta-catenin transgenes. Although activated Wnt signaling also resulted in larger numbers of Ag-specific memory CD4 T cells, their functional attributes and expansion after the secondary infection were not improved. Thus, constitutive activation of the canonical Wnt pathway favors memory CD8 T cell formation during initial immunization, resulting in enhanced immunity upon second encounter with the same pathogen.

B and T lymphocyte attenuator regulates CD8+ T cell-intrinsic homeostasis and memory cell generation.

B and T lymphocyte attenuator (BTLA) is a negative regulator of T cell activation, but its function in vivo is not well characterized. Here we show that mice deficient in full-length BTLA or its ligand, herpesvirus entry mediator, had increased number of memory CD8(+) T cells. The memory CD8(+) T cell phenotype resulted from a T cell-intrinsic perturbation of the CD8(+) T cell pool. Naive BTLA-deficient CD8(+) T cells were more efficient than wild-type cells at generating memory in a competitive antigen-specific system. This effect was independent of the initial expansion of the responding antigen-specific T cell population. In addition, BTLA negatively regulated antigen-independent homeostatic expansion of CD4(+) and CD8(+) T cells. These results emphasize two central functions of BTLA in limiting T cell activity in vivo.

Memory of Recessions

This paper reviews the evidence on the effects of recessions on potential output. In contrast to the assumption in mainstream macroeconomic models that economic fluctuations do not change potential output paths, the evidence is that they do in the case of recessions. A model is proposed to explain this phenomenon, based on an analogy with water flows in porous media. Because of the discrete adjustments made by heterogeneous economic agents in such a world, potential output displays hysteresis with regard to aggregate demand shocks, and thus retains a memory of the shocks associated with recessions.

Ghosts in contemporary African diasporic literature : re-visioning history, memory and identity

Starting from the observation that ghosts are strikingly recurrent and prominent figures in late-twentieth African diasporic literature, this dissertation proposes to account for this presence by exploring its various functions. It argues that, beyond the poetic function the ghost performs as metaphor, it also does cultural, theoretical and political work that is significant to the African diaspora in its dealings with issues of history, memory and identity. Toni Morrison's Beloved (1987) serves as a guide for introducing the many forms, qualities and significations of the ghost, which are then explored and analyzed in four chapters that look at Fred D'Aguiar's Feeding the Ghosts (1998), Gloria Naylor's Mama Day (1988), Paule Marshall's Praisesong for the Widow (1983) and a selection of novels, short stories and poetry by Michelle Cliff. Moving thematically through these texts, the discussion shifts from history through memory to identity as it examines how the ghost trope allows the writers to revisit sites of trauma; revise historical narratives that are constituted and perpetuated by exclusions and invisibilities; creatively and critically repossess a past marked by violence, dislocation and alienation and reclaim the diasporic culture it contributed to shaping; destabilize and deconstruct the hegemonic, normative categories and boundaries that delimit race or sexuality and envision other, less limited and limiting definitions of identity. These diverse and interrelated concerns are identified and theorized as participating in a project of "re-vision," a critical project that constitutes an epistemological as much as a political gesture. The author-based structure allows for a detailed analysis of the texts and highlights the distinctive shapes the ghost takes and the particular concerns it serves to address in each writer's literary and political project. However, using the ghost as a guide into these texts, taken collectively, also throws into relief new connections between them and sheds light on the complex ways in which the interplay of history, memory and identity positions them as products of and contributions to an African diasporic (literary) culture. If it insists on the cultural specificity of African diasporic ghosts, tracing its origins to African cultures and spiritualities, the argument also follows gothic studies' common view that ghosts in literary and cultural productions-like other related figures of the living dead-respond to particular conditions and anxieties. Considering the historical and political context in which the texts under study were produced, the dissertation makes connections between the ghosts in them and African diasporic people's disillusionment with the broken promises of the civil rights movement in the United States and of postcolonial independence in the Caribbean. It reads the texts' theoretical concerns and narrative qualities alongside the contestation of traditional historiography by black and postcolonial studies as well as the broader challenge to conventional notions such as truth, reality, meaning, power or identity by poststructuralism, postcolonialism or queer theory. Drawing on these various theoretical approaches and critical tools to elucidate the ghost's deconstructive power for African diasporic writers' concerns, this work ultimately offers a contribution to "speciality studies," which is currently emerging as a new field of scholarship in cultural theory.

Memory and effector CD8 T-cell responses after nanoparticle vaccination of melanoma patients.

Induction of cytotoxic CD8 T-cell responses is enhanced by the exclusive presentation of antigen through dendritic cells, and by innate stimuli, such as toll-like receptor ligands. On the basis of these 2 principles, we designed a vaccine against melanoma. Specifically, we linked the melanoma-specific Melan-A/Mart-1 peptide to virus-like nanoparticles loaded with A-type CpG, a ligand for toll-like receptor 9. Melan-A/Mart-1 peptide was cross-presented, as shown in vitro with human dendritic cells and in HLA-A2 transgenic mice. A phase I/II study in stage II-IV melanoma patients showed that the vaccine was well tolerated, and that 14/22 patients generated ex vivo detectable T-cell responses, with in part multifunctional T cells capable to degranulate and produce IFN-γ, TNF-α, and IL-2. No significant influence of the route of immunization (subcutaneous versus intradermal) nor dosing regimen (weekly versus daily clusters) could be observed. It is interesting to note that, relatively large fractions of responding specific T cells exhibited a central memory phenotype, more than what is achieved by other nonlive vaccines. We conclude that vaccination with CpG loaded virus-like nanoparticles is associated with a human CD8 T-cell response with properties of a potential long-term immune protection from the disease.

A test of long memory hypothesis based on self-similarity

This paper develops a new test of true versus spurious long memory, based on log-periodogram estimation of the long memory parameter using skip-sampled data. A correction factor is derived to overcome the bias in this estimator due to aliasing. The procedure is designed to be used in the context of a conventional test of significance of the long memory parameter, and composite test procedure described that has the properties of known asymptotic size and consistency. The test is implemented using the bootstrap, with the distribution under the null hypothesis being approximated using a dependent-sample bootstrap technique to approximate short-run dependence following fractional differencing. The properties of the test are investigated in a set of Monte Carlo experiments. The procedure is illustrated by applications to exchange rate volatility and dividend growth series.

Reading Ng Kim Chew: Malaysian-Chineseness and memory in contemporary Malaysian Chinese literature in taiwan

The idea of Chineseness as a geographic, cultural-specific and ethnically-charged concept, and the pivotal role assumed by memory linger throughout the writings of most authors hailing from Chinese community in Southeast Asia. Among these communities, being the Malaysian Chinese the more prolific in terms of number of writers and pieces of literature produced, this paper deals specifically with it. Its focus is put on the literature produced by Malaysian Chinese authors residing in Taiwan, which topic constitutes an important part of the first chapter, and on one of its main representatives, Ng Kim Chew, to whom chapter two and three are fully dedicated. A literary analysis of one of his short stories, Huo yu tu, will allow the reader to have a first-hand experience, through excerpts from the original text, of the importance of Chineseness and memory in the literary production of Ng and of many authors sharing with him similar life and literary experiences. I started this research from the assumption that these authors make large use of their own memories and memories from their own community in their writing as a way to re-tie themselves to the Chineseness they left in their places of origin. However in the case of Ng Kim Chew, the analysis of his works led be to theorizing that the identity he is imbued with, if there is one, is not Chinese, nor Malaysian, but purely and distinctively Malaysian-Chinese. This paper can also serve as an introduction for the general public to the field of Sinophone literature from Southeast Asia and to promote wider and innovative paths of research within the realm of Chinese studies that go beyond China proper.

Characterization of Melan-A reactive memory CD8+ T cells in a healthy donor.

Melan-A specific CD8+ T cells are thought to play an important role against the development of melanoma. Their in vivo expansion is often observed with advanced disease. In recent years, low levels of Melan-A reactive CD8+ T cells have also been found in HLA-A2 healthy donors, but these cells harbor naive characteristics and are thought to be mostly cross-reactive for the Melan-A antigen. Here, we report on a large population of CD8+ T cells reactive for the Melan-A antigen, identified in one donor with no evidence of melanoma. Interestingly, this population is oligoclonal and displays a clear memory phenotype. However, a detailed study of these cells indicated that they are unlikely to be directly specific for melanoma, so that their in vivo expansion may have been driven by an exogenous antigen. Screening of a Melan-A cross-reactive peptide library suggested that these cells may be specific for an epitope derived from a Mycobacterium protein, which would provide a further example of CD8+ T cell cross-reactivity between a pathogen antigen and a tumor antigen. Finally, we discuss potential perspectives regarding the role of such cells in heterologous immunity, by influencing the balance between protective immunity and pathology, e.g. in the case of melanoma development.

Memory in contracts: the experience of the EBRD (1991-2003)

The objective of this paper is to identify the role of memory as a screening device in repeated contracts with asymmetric information in financial intermediation. We use an original dataset from the European Bank for Reconstruction and Development. We propose a simple empirical method to capture the role of memory using the client's reputation. Our results unambiguously isolate the dominant effect of memory on the bank's lending decisions over market factors in the case of established clients.

Selective bystander proliferation of memory CD4+ and CD8+ T cells upon NK T or T cell activation.

Ag-experienced or memory T cells have increased reactivity to recall Ag, and can be distinguished from naive T cells by altered expression of surface markers such as CD44. Memory T cells have a high turnover rate, and CD8(+) memory T cells proliferate upon viral infection, in the presence of IFN-alphabeta and/or IL-15. In this study, we extend these findings by showing that activated NKT cells and superantigen-activated T cells induce extensive bystander proliferation of both CD8(+) and CD4(+) memory T cells. Moreover, proliferation of memory T cells can be induced by an IFN-alphabeta-independent, but IFN-gamma- or IL-12-dependent pathway. In these conditions of bystander activation, proliferating memory (CD44(high)) T cells do not derive from activation of naive (CD44(low)) T cells, but rather from bona fide memory CD44(high) T cells. Together, these data demonstrate that distinct pathways can induce bystander proliferation of memory T cells.

As the world turns: short-term human spatial memory in egocentric and allocentric coordinates

We aimed to determine whether human subjects' reliance on different sources of spatial information encoded in different frames of reference (i.e., egocentric versus allocentric) affects their performance, decision time and memory capacity in a short-term spatial memory task performed in the real world. Subjects were asked to play the Memory game (a.k.a. the Concentration game) without an opponent, in four different conditions that controlled for the subjects' reliance on egocentric and/or allocentric frames of reference for the elaboration of a spatial representation of the image locations enabling maximal efficiency. We report experimental data from young adult men and women, and describe a mathematical model to estimate human short-term spatial memory capacity. We found that short-term spatial memory capacity was greatest when an egocentric spatial frame of reference enabled subjects to encode and remember the image locations. However, when egocentric information was not reliable, short-term spatial memory capacity was greater and decision time shorter when an allocentric representation of the image locations with respect to distant objects in the surrounding environment was available, as compared to when only a spatial representation encoding the relationships between the individual images, independent of the surrounding environment, was available. Our findings thus further demonstrate that changes in viewpoint produced by the movement of images placed in front of a stationary subject is not equivalent to the movement of the subject around stationary images. We discuss possible limitations of classical neuropsychological and virtual reality experiments of spatial memory, which typically restrict the sensory information normally available to human subjects in the real world.

A homing procedure for studying spatial memory in immature and adult rodents

In this procedure, subjects learn the spatial position of one hole out of many, that allows them to escape from a large open-field into their home cage. The arena is circular and can be rotated between trials so that no proximal landmark is permanently associated with the target hole. This task is thus similar to the Morris water maze procedure, since subjects must remember the position of the escape hole relative to extra-arena cues only. In addition it allows studying the importance of olfactory cues such as scent marks in or around a hole. Since the motivation is to reach home and the motor requirement is low, this task provides a useful alternative to the Morris place navigation task for studying spatial orientation in weanling or senescent rats. Examples are given showing that various behavioural parameters provide a good estimation as how subjects learn this task.