Memory retrieval time and memory capacity of the CA3 network: role of gamma frequency oscillations

The existence of recurrent synaptic connections in CA3 led to the hypothesis that CA3 is an autoassociative network similar to the Hopfield networks studied by theorists. CA3 undergoes gamma frequency periodic inhibition that prevents a persistent attractor state. This argues against the analogy to Hopfield nets, in which an attractor state can be used for working memory. However, we show that such periodic inhibition allows one cycle of recurrent excitatory activity and that this is sufficient for memory retrieval (within milliseconds). Thus, gamma oscillations are compatible with a long-term autoassociative memory function for CA3. A second goal of our work was to evaluate previous methods for estimating the memory capacity (P) of CA3. We confirm the equation, P = c/a(2), where c is the probability that any two cells are recurrently connected and a is the fraction of cells representing a memory item. In applying this to CA3, we focus on CA3a, the subregion where recurrent connections are most numerous (c = 0.2) and approximate randomness. We estimate that a memory item is represented by approximately 225 of the 70,000 neurons in CA3a (a = 0.003) and that approximately 20,000 memory items can be stored. Our general conclusion is that the physiological and anatomical findings of CA3a are consistent with an autoassociative function. The nature of the information that is associated in CA3a is discussed. We also discuss how the autoassociative properties of CA3 and the heteroassociative properties of dentate synapses (linking sequential memories) form an integrated system for the storage and recall of item sequences. The recall process generates the phase precession in dentate, CA3, and entorhinal cortex.     

An experimental test of a game‐theoretical model of reciprocity

In this contribution the norm of reciprocity is defined as a basic internal motivation. Using formal tools of game theory, a model of social utility function is presented. The reciprocity model predicts that social actors should reciprocate costs and benefits they receive, even when there are costs in conforming to the norm. Hypotheses about actors' behavior, expectations and evaluations are derived from the model. The hypotheses were tested in an experimental situation, the reciprocity game, consisting of a prisoner's dilemma game (PD) followed by a dictator game (DG). The sample was composed of 74 Italian undergraduate students. In line with the model's predictions, the experimental results showed that participants reciprocate the behavior of the opponent in the PD. In the DG, if the opponent cooperated, participants gave back an almost equal share, whereas if the opponent defected, participants gave a minimal amount. These reciprocity effects are modulated by individual differences in the concern for reciprocity. Copyright © 2000 John Wiley & Sons, Ltd.     

Exploring temporal aspects of social identity: the concept of possible social identities

In the social identity model of reactions to negative social identity (Tajfel & Turner, 1979, 1986), the concept of cognitive alternatives focuses on individual and group perceptions of the possibility of changing group memberships or improving existing ones. In the current paper, the under-researched concept of cognitive alternatives is expanded so as to better encompass issues relating to the temporal dimension of social identity maintenance. Markus and Nurius' (1986) possible selves perspective is used as a starting point for exploring the manner in which social identity maintenance is influenced by cognitions about, and social representations of, a group's past and possible future. It is proposed that the concept of cognitive alternatives be expanded to incorporate possible social identities, which represent individual and shared cognitions about possible past group memberships, possible future group memberships, and perceptions of the possible past and future for current group memberships. The consequences of perceiving positive and negative possible social identities are examined, and methodological issues which might facilitate their empirical study addressed. © 1998 John Wiley & Sons, Ltd.     

Social exclusion lowers working memory capacity in gay-men but not in heterosexual-men

Because sexual orientation is a crucial factor in social discrimination, this study assessed how the working memory capacity of gay-men and heterosexual-men is affected by a social exclusion event (N = 88). To manipulate the experience of social exclusion participants were included or excluded from a game of Cyberball. To assess working memory capacity, participants had to recall a series of letters while performing math problems in an automated version of the operation span task. The results of this small study, showed the sexual orientation of participants interacted with variations in belonging such that being ostracized (but not being included) lowered the working memory capacity of gay-men relative to heterosexual-men. Implications for research on belonging, social exclusion, and stereotype threat are discussed.     

Step changes in the intertrial interval in the midsession reversal task: Predicting pigeons' performance with the learning-to-time model

Our goal was to assess the role of timing in pigeons' performance in the midsession reversal task. In discrete-trial sessions, pigeons learned to discriminate between 2 stimuli, S1 and S2. Choices of S1 were reinforced only in the first half of the session and choices of S2 were reinforced only in the second half. Typically, pigeons choose S2 before the contingency reverses (anticipatory errors) and S1 after (perseverative errors), suggesting that they time the interval from the beginning of the session to the contingency reversal. To test this hypothesis, we exposed pigeons to a midsession reversal task and, depending on the group, either increased or decreased the ITI duration. We then contrasted the pigeons' performance with the predictions of the Learning-to-Time (LeT) model: In both conditions, preference was expected to reverse at the same time as in the previous sessions. When the ITI was doubled, pigeons' preference reversal occurred at half the trial number but at the same time as in the previous sessions. When the ITI was halved, pigeons' preference reversal occurred at a later trial but at an earlier time than in the previous sessions. Hence, pigeons' performance was only partially consistent with the predictions of LeT, suggesting that besides timing, other sources of control, such as the outcome of previous trials, seem to influence choice.     

Relations between self-leadership and scores on the Big Five

The recent construct of Self-leadership, which includes cognitive and behavioral strategies of managing oneself, has yet to be examined for associations with central personality dimensions such as the Big Five and their higher-order factors (Alpha, Beta). It was hypothesized that Self-leadership and its subfacets would be significantly correlated with all Big Five traits except Agreeableness, albeit higher with Extraversion and Openness to Experiences as it should pertain more strongly to agentic than communal traits. Analyses in university students (N=168) indicated that Self-leadership and its facets were more strongly related to Beta (Agency) than Alpha (Communion), and, although there were mostly positive correlations, Self-leadership should be distinguished from the Big Five traits. Findings are discussed regarding Self-leadership's associations with the Big Five traits and higher-order factors.     

Through neural stimulation to behavior manipulation: a novel method for analyzing dynamical cognitive models

The dynamical systems' approach to cognition (Dynamicism) promises computational models that effectively embed cognitive processing within its more natural behavioral context. Dynamical cognitive models also pose difficult, analytical challenges, which motivate the development of new analytical methodology. We start by illustrating the challenge by applying two conventional analytical methods to a well-known Dynamicist model of categorical perception. We then introduce our own analysis, which works by analogy with neural stimulation methods, and which yields some novel insights into the way the model works. We then extend and apply the method to a second Dynamicist model, which captures the key psychophysical trends that emerge when humans and animals compare two numbers. The results of the analysis-which reveals units with tuning functions that are monotonically related to the magnitudes of the numbers that the agents must compare-offer a clear contribution to the contentious debate concerning the way number information is encoded in the brain.