Motivational State and Reward Content Determine Choice Behavior under Risk in Mice

Risk is a ubiquitous feature of the environment for most organisms, who must often choose between a small and certain reward and a larger but less certain reward. To study choice behavior under risk in a genetically well characterized species, we trained mice (C57BL/6) on a discrete trial, concurrent-choice task in which they must choose between two levers. Pressing one lever (safe choice) is always followed by a small reward. Pressing the other lever (risky choice) is followed by a larger reward, but only on some of the trials. The overall payoff is the same on both levers. When mice were not food deprived, they were indifferent to risk, choosing both levers with equal probability regardless of the level of risk. In contrast, following food or water deprivation, mice earning 10% sucrose solution were risk-averse, though the addition of alcohol to the sucrose solution dose-dependently reduced risk aversion, even before the mice became intoxicated. Our results falsify the budget rule in optimal foraging theory often used to explain behavior under risk. Instead, they suggest that the overall demand or desired amount for a particular reward determines risk preference. Changes in motivational state or reward identity affect risk preference by changing demand. Any manipulation that increases the demand for a reward also increases risk aversion, by selectively increasing the frequency of safe choices without affecting frequency of risky choices

Self-esteem and memory in aging, mild cognitive impairment and Alzheimer’s disease : examinations and analyses of the self-reference effect

Le premier objectif de cette thèse était d’explorer l’effet de référence à soi (ERS) sur la mémoire dans le vieillissement, l’amnestic Mild Cognitive Impairment (aMCI) et la maladie d’Alzheimer (MA) à un stade précoce de l’évolution. Le second fut de revisiter les théories actuelles pour expliquer ce bénéfice mnésique, puis de tenter d’élucider ses mécanismes. Nous avons montré que l’ERS sur les représentations sémantiques de ses propres traits de personnalité (qui est une composante de notre identité) était préservé dans le vieillissement. Par ailleurs, nous avons montré que la profondeur de traitement, longtemps considérée comme le processus sous-tendant l’ERS, n’intervenait pas dans ce dernier. A contrario, l’interaction de l’âge et de l’estime de soi, ainsi que les expériences de vie des individus modulaient l’ERS. Nous avons montré que l’ERS pouvait résulter de deux processus : celui de la consistance des traits de caractère et celui de l’élaboration automatique des traits de caractère avec l’identité des individus. Nous avons par ailleurs rapporté pour la première fois que ce bénéfice mnésique s’opérait chez des patients atteints d’aMCI, un stade symptomatique et pré-démentiel de la MA, et qu’il pouvait s’observer dans une moindre mesure chez des patients MA. En outre, l’ERS agit comme mécanisme de self-défense chez les patients aMCI et MA, en les protégeant d’informations menaçantes pour l’intégrité de leur soi. Nous suggérons en dernier lieu que la référence à soi pourrait servir d’outil de réhabilitation sociale ou clinique pour augmenter l’estime de soi de certains individus et préserver leur mémoire et leur bien-être.The first aim of this thesis was to examine the self-reference effect (SRE) on memory in aging, amnestic mild cognitive impairment (aMCI) and early-stage of Alzheimer’s disease (AD). The second aim was to review the whole literature on the SRE and to attempt understanding its mechanisms. We showed that the SRE on semantic summary representations of one’s traits (which is a component of identity) was preserved in aging. Besides, we showed that depth of processing, which was hitherto regarded as the mechanism responsible for the SRE, did not actually play a role in the latter. By contrast, the interaction of age and self-esteem, as well as individuals’ life experiences modulated the SRE. We showed that the SRE resulted from two processes: the congruency of traits as well as the elaboration of traits with individuals’ identity. We also reported for the first time that aMCI patients benefited from the SRE, as well as AD patients in the early stage of the disease to a lesser extent. Furthermore, the SRE acted as a self-defense mechanism in patients with aMCI and AD by protecting them from negative feedback that constituted a threat to the integrity of their selves. Finally, we suggest that referencing the self could serve as a tool for social or clinical rehabilitation programs, by increasing the self-esteem of some individuals and preserving their memory and well-being

Estime de soi et mémoire dans le vieillissement, le mild cognitive impairment et la maladie d’Alzheimer : explorations et analyses de l’effet de référence à soi

The first aim of this thesis was to examine the self-reference effect (SRE) on memory in aging, amnestic mild cognitive impairment (aMCI) and early-stage of Alzheimer’s disease (AD). The second aim was to review the whole literature on the SRE and to attempt understanding its mechanisms. We showed that the SRE on semantic summary representations of one’s traits (which is a component of identity) was preserved in aging. Besides, we showed that depth of processing, which was hitherto regarded as the mechanism responsible for the SRE, did not actually play a role in the latter. By contrast, the interaction of age and self-esteem, as well as individuals’ life experiences modulated the SRE. We showed that the SRE resulted from two processes: the congruency of traits as well as the elaboration of traits with individuals’ identity. We also reported for the first time that aMCI patients benefited from the SRE, as well as AD patients in the early stage of the disease to a lesser extent. Furthermore, the SRE acted as a self-defense mechanism in patients with aMCI and AD by protecting them from negative feedback that constituted a threat to the integrity of their selves. Finally, we suggest that referencing the self could serve as a tool for social or clinical rehabilitation programs, by increasing the self-esteem of some individuals and preserving their memory and well-being.Le premier objectif de cette thèse était d’explorer l’effet de référence à soi (ERS) sur la mémoire dans le vieillissement, l’amnestic Mild Cognitive Impairment (aMCI) et la maladie d’Alzheimer (MA) à un stade précoce de l’évolution. Le second fut de revisiter les théories actuelles pour expliquer ce bénéfice mnésique, puis de tenter d’élucider ses mécanismes. Nous avons montré que l’ERS sur les représentations sémantiques de ses propres traits de personnalité (qui est une composante de notre identité) était préservé dans le vieillissement. Par ailleurs, nous avons montré que la profondeur de traitement, longtemps considérée comme le processus sous-tendant l’ERS, n’intervenait pas dans ce dernier. A contrario, l’interaction de l’âge et de l’estime de soi, ainsi que les expériences de vie des individus modulaient l’ERS. Nous avons montré que l’ERS pouvait résulter de deux processus : celui de la consistance des traits de caractère et celui de l’élaboration automatique des traits de caractère avec l’identité des individus. Nous avons par ailleurs rapporté pour la première fois que ce bénéfice mnésique s’opérait chez des patients atteints d’aMCI, un stade symptomatique et pré-démentiel de la MA, et qu’il pouvait s’observer dans une moindre mesure chez des patients MA. En outre, l’ERS agit comme mécanisme de self-défense chez les patients aMCI et MA, en les protégeant d’informations menaçantes pour l’intégrité de leur soi. Nous suggérons en dernier lieu que la référence à soi pourrait servir d’outil de réhabilitation sociale ou clinique pour augmenter l’estime de soi de certains individus et préserver leur mémoire et leur bien-être

Reducing alcohol concentration reduces risk aversion.

<p>A. Experienced reward variance. Error bars indicate standard error of the means (SEM). Sucrose = 10% sucrose; alcohol = 10% sucrose and 20% ethanol. B. Risk preference of mice when the concentration of alcohol was manipulated. Alcohol dose-dependently reduced risk aversion. C. Number of presses. The addition of alcohol to the sucrose reward dose-dependently reduced the number of safe choices. D. Increasing alcohol concentration increased choice latency. E. Rate of lever pressing during the last session.</p

With free access to food and water, mice were indifferent to risk.

<p>A. Experienced risk measured by reward variance. The actual experienced risk is calculated by counting the safe reward size (0.01 ml) as 1. When the trial is unrewarded, the outcome is 0, when the outcome is 0.02 ml or twice the safe reward size, the outcome is counted as 2. Error bars indicate standard error of the means (SEM). Sucrose = 10% sucrose; alcohol = 10% sucrose and 20% ethanol. B. Risk preference under different levels of risk (average of last 3 sessions; probability of reward on the risky lever = 12.5%). Mice were trained successively on 4 levels of risk (100%, 0.01 ml; 50%, 0.02 ml; 25%, 0.04 ml; 12.5%, 0.08 ml). Risk aversion index was calculated by dividing number of safe choices by the total number of presses. If the index is greater than 0.5, the animal is risk averse; if it is less than 0.5, the animal is risk prone. C. Number of presses on the two levers (average of last 3 sessions; probability of reward on the risky lever = 12.5%). D. Rate of lever pressing during the last session.</p

Reward reversal.

<p>To demonstrate that the effects we observed were due to the identity of the reward outcome, we also reversed the identity of the reward (sucrose to alcohol and alcohol to sucrose). A. Experienced reward variance on the risky lever average of last 3 sessions at 12.5%). B. Risk preference (average of last 3 sessions at 12.5%). The sucrose group displayed higher risk aversion, whereas the alcohol group was risk neutral. C. Total presses on the two levers (average of last 3 sessions at 12.5%). D. Rate of lever pressing in a session (average of last 3 sessions at 12.5%).</p

Cumulative records of lever pressing under different conditions.

<p>Data from 4 mice are shown from left to right: 2 receiving 10% sucrose solution (sucrose), and 2 receiving 10% sucrose plus 20% alcohol (alcohol). Each graph shows data from the last session (12.5%). The identity of the reward (sucrose = 10% sucrose solution; alcohol = 10% sucrose plus 20% ethanol) and the animal number are shown on top.</p

Effects of motivational state and reward content on risk preference.

<p>A. Experienced reward variance on the risky lever after water deprivation (average of last 3 sessions; probability of reward on the risky lever = 12.5%). Error bars indicate standard error of the means (SEM). Sucrose = 10% sucrose; alcohol = 10% sucrose and 20% ethanol. B. Risk preference after water deprivation. The sucrose group displayed higher risk aversion, whereas the alcohol group was risk neutral. C. Number of presses on the two levers (average of last 3 sessions). .D. Rate of lever pressing during the last session. E. Experienced reward variance on the risky lever after food deprivation (12.5%). F. Risk preference after food deprivation. The sucrose group displayed higher risk aversion, whereas the alcohol group was risk neutral. G. Total number of lever presses in a session (average of last 3 sessions). H. Rate of lever pressing during the last session (12.5%). I. Choice latency (the time it takes the animal to press the lever once the trial starts). After either food or water deprivation, sucrose group showed much shorter latency compared with the alcohol group (12.5%, average of last 3 sessions).</p

Lever reversal.

<p>A. Experienced reward variance on the risky lever (average of last 3 sessions; probability of reward on the risky lever = 12.5%). To control for the lever used, the previously safe lever became the risky lever, and the previously risky lever became the safe lever. Error bars indicate standard error of the means (SEM). Sucrose = 10% sucrose; alcohol = 10% sucrose and 20% ethanol. B. Risk preference after water deprivation (average of last 3 sessions at 12.5%). The sucrose group displayed higher risk aversion, whereas the alcohol group was risk neutral. C. Presses on the left lever: from safe to risky (average of last 3 sessions at 12.5%). The sucrose group decreased pressing on the lever once it switched from safe to risky (100% probability of 1 reward to 12.5% probability of 8 rewards), but the alcohol group did not. D. Presses on the right lever: from risky to safe average of last 3 sessions at 12.5%). The sucrose group increased pressing on the lever once it switched from risky to safe (12.5% probability of 8 rewards to 100% probability of 1 reward), but the alcohol group did not. E. The time course of lever reversal. Rate of lever pressing during the first, fourth, and ninth session.</p

Illustration of the behavioral task.

<p>Illumination of the chamber and insertion of both levers signaled the start of the trial. Choosing the safe lever always resulted in an immediate and constant reinforcement (0.01 ml). Choosing the risky lever resulted in a more variable outcome, while maintaining the same overall payoff (e.g. 50% chance of 0.02 ml). Following each choice, both levers were retracted and the light was turned off. The next trial started 10 seconds later (inter-trial interval, ITI).</p