Two Choice Social Decision Making Task

Introduction

Scheggie et al (2022) described the apparatus and experimental setup employed to investigate how reciprocal connections between the cortex and amygdala influence prosocial and selfish decision-making in mice. The Two Choice Decision Making Task aimed to simulate social interactions and decision-making scenarios in a controlled environment. The following factors were considered in the creation of this behavioral task:

1. Behavioral Choices: The Two Choice Decision Making Task allows researchers to observe and record the choices made by the actor mice in situations where they could engage in prosocial behaviors (rewarding both themselves and the recipient) or selfish behaviors (prioritizing their own rewards).
2. Social Interactions: The mesh separation wall enables social exploration and nose-to-nose interactions between the mice. This aspect was critical for understanding the dynamics of social decision-making.
3. Quantitative Data: The food magazines and rewards are used as quantifiable outcomes, allowing the researchers to analyze the frequency and patterns of prosocial and selfish choices made by the actor mice.
4. Controlled Environment: The controlled experimental environment ensured that potential biases arising from variations in external conditions were minimized, allowing researchers to attribute observed behaviors more reliably to the specific experimental conditions.

Apparatus and Equipment

Actor's Compartment (the standard Operant Chamber):

• Dimensions: Length (L): 24 cm, Width (W): 20 cm, Height (H): 18.5 cm.
• The actor's compartment is designed to house one of the mice (the actor).
• It contains two nose-poke holes and a food magazine.
• The actor interacts with the nose poke holes and receives rewards.

Recipient's Compartment (Triangle-Shaped Chamber):

• Dimensions: L: 18 cm, W: 14 cm, H: 18.5 cm.
• The recipient's compartment is composed of a  small triangle-shaped chamber.
• This compartment contains a food magazine connected to a food dispenser, allowing the recipient to receive food rewards as per the actor

Mesh Separation Wall:

• The metal mesh separation wall is located between the actor's and the recipient's compartments.
• The mesh has holes measuring 1 cm in diameter.
• This mesh allows for social exploration and nose-to-nose interaction between the actor and the recipient while maintaining a physical barrier.

Rodent location and behavior can be tracked using a video tracking software package such as Noldus EthoVision, ANY-Maze, or BehaviorCloud.

Training Protocol

As per Scheggia et al (2022)

Experimental Environment:

• The entire setup was placed inside a sound-attenuating cubicle to minimize external environmental influences.
• The cubicle was homogeneously and dimly lit to maintain consistent lighting conditions (6 ± 1 lux) and prevent gradients in light, temperature, and sound.
• The controlled environment aimed to prevent any biases that could result from differences in sensory conditions.
• The actors and recipients were mildly food-restricted and housed together before the experiment. Unfamiliar recipients were used for specific conditions.

Task design

The task design included three conditions:

• With recipient (cagemate)
• No recipient (empty compartment)
• With a toy (inanimate object).

The actor could make selfish choices (receive reward alone) or altruistic choices (share reward with the recipient) by poking into left or right nose poke holes. Both choices were reinforced with a food reward delivery, and the order of choices was balanced. After each nose poke, a 5-second interval occurred.

Testing

Actors were tested for five days in 40-minute sessions, either with a cagemate, no recipient, or a toy. In some conditions, an opaque or transparent partition was used between the actor and recipient to control visual and social cues. The setup was monitored by a digital camera connected to a behavioral tracking system.

Fixed ratio schedules

This protocol involved testing mice's voluntary choices to benefit others under increasing fixed ratio (FR) schedules for altruistic decisions. The FR schedule for altruistic decisions ranged from FR2 to FR8, meaning that the number of responses required to give food to the recipient increased each day (from 2 to 8 responses). Selfish responses were consistently reinforced on an FR1 schedule. In the 'no recipient' condition, each actor's preferred nose poke was reinforced using the increasing FR schedule, while the other nose poke remained on an FR1 schedule. This setup aimed to investigate whether subject would continue to make altruistic choices even when the effort required was higher, and it included controls without a recipient to isolate the effects of the schedule.

SDM task without concurrent reward

In this phase of the study, mice were initially trained in the social decision-making (SDM) task. The task was then altered, so that one nose poke led to food rewards exclusively for the mice themselves (selfish choice), while the other nose poke resulted in food rewards solely for the recipient (altruistic choice). During testing, the mice were engaged in longer sessions lasting 120 minutes, allowing researchers to observe whether the mice's choices were influenced by feelings of satiety over an extended period of time.

Satiety-induced reward devaluation

In this phase of the study, mice were subjected to satiety-induced reward devaluation tests. After undergoing five days of the social decision-making (SDM) task, the mice were individually housed for two hours and allowed to consume reward pellets to the point of satiety in their cages. Following this, they were moved to the operant chamber and tested in a session without reinforcement.

Two experiments were conducted with sated actor mice:

In Experiment 1, two groups were tested: one where neither the actor nor the recipient received rewards ('no reward'), and the other where actor mice did not receive reinforcement, but could still allocate food rewards to their recipients ('reward to recipient only').
In Experiment 2, mice were tested in the 'SDM without concurrent reward' condition after making altruistic choices in the initial SDM task.

SDM task with sated recipients

In this part of the study, the social decision-making (SDM) task was modified to include sated recipients. Both actor and recipient mice were subjected to food restriction. Prior to each session of the SDM task, recipient mice were separated from their cage mates (actors) and were fed to satiety, providing them with free access to reward pellets in their own cages. Subsequently, both actor and recipient mice were moved to the operant chamber and were tested in a session with reinforcement.

In a separate group of mice, satiety-induced reward devaluation was also tested in recipient mice after they had undergone standard training in the SDM task for five days. In this scenario, one group of actor mice was tested with food-restricted recipients, and another group with sated recipients following the reward devaluation induced by satiety.

Data Analysis

The following parameters can be observed using the Two Choice Social Decision Making task:

• Decision Preference Scores: The ratio of altruistic to selfish choices made by the subjects with the ability to assess scores over time, between different experimental groups, and under different conditions.
• Choice Behavior:  The number of altruistic and selfish choices made by the subjects. This includes analysis of the frequency and pattern of nose pokes in response to different cues.
• Learning and Training: How subjects acquire and develop their decision-making preferences over the course of training.
• Effects of Recipient Familiarity: Examining the actor's response to familiar and unfamiliar recipients and the influences on decision-making behavior.
• Impact of Social Hierarchy: The study of the impact of social dominance hierarchy on decision-making through the comparison of the choices of dominant and subordinate mice.
• Effects of Neuronal Manipulation: The addition of chemogenetic techniques to manipulate neural activity alongside the use of this apparatus is possible to study the causal relationship between specific brain regions (such as BLA and PFC) and decision-making behaviors.
• Neural Activity Patterns: The use of fiber photometry can be added to study real-time neural activity patterns in brain regions related to decision-making. This can provide insights into the neural mechanisms underlying social behaviors.
• Influence of Reward Devaluation: Subjects can be examined for satiety-induced reward devaluation. This allows researchers to study how changes in reward value influence decision-making.
• Effect of Social Exploration: The study of social exploration behaviors between subjects and how this interaction relates to decision preferences.
• Effects of Sex and Gender: The exploration of sex and gender influence decision-making behaviors.
• Impact of Altruistic Choices on Recipients: The study the outcomes and responses of recipients when subjects make altruistic choices.

Summary

 The Two Choice Social Decision Making apparatus allows for the quantitative analysis iofe social decision-making behaviors in rodents, allowing subjects to make choices between altruistic and selfish actions. The subjects are trained in a Social Decision-Making (SDM) task, which involves nose-poking at different locations to make choices. The choices are either altruistic, benefiting another subject, or selfish, leading to personal rewards.

The apparatus allows researchers to manipulate various factors and conditions to understand the neural and behavioral mechanisms underlying social decision-making. The examination of altruistic and selfish choices of subjects can be observed with the following parameters:

• The observation of social preferences over time.
• How familiarity with the recipient influences decision-making behavior.
• The analysis of decisions of dominant and subordinate subjects and the impact of social hierarchy on decision-making.
•  Neural manipulation and neural activity patterns and techniques to study the relationship between specific brain regions and decision-making.
• The examination of how changes in the value of rewards influence decision preferences.
• The apparatus enables the study of social interactions between subjects, both with recipients and other actors, and how these interactions relate to decision preferences.
• The influence of gender differences on decision-making behaviors.

Overall, the apparatus provides a controlled environment to investigate the factors that drive altruistic and selfish decision-making in rodents, shedding light on the neural circuits and behavioral processes underlying social interactions and cooperative behaviors.

References

Scheggia, D., La Greca, F., Maltese, F., Chiacchierini, G., Italia, M., Molent, C., Bernardi, F., Coccia, G., Carrano, N., Zianni, E., Gardoni, F., Di Luca, M., & Papaleo, F. (2022). Reciprocal cortico-amygdala connections regulate prosocial and selfish choices in mice. Nature Neuroscience, 25(11), 1505-1518. https://doi.org/10.1038/s41593-022-01179-2

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