Delay Discounting

The delay discounting task measures impulsive choice by presenting rodents with repeated decisions between a small-immediate reward and a larger reward delivered after an escalating delay. The apparatus consists of an operant chamber with two response levers, a pellet dispenser, and a house light, configured so that one lever always delivers one pellet immediately while the other delivers three or four pellets after a programmed delay. Performance recruits orbitofrontal cortex (OFC), nucleus accumbens (NAc), and basolateral amygdala circuits that encode subjective reward value as a function of temporal distance. Steeper discounting reflects greater impulsivity and has translational relevance to addiction, ADHD, and obesity phenotypes.

The primary dependent variable is the indifference point at each delay, defined as the adjusted amount at which the subject switches preference from delayed to immediate reward. Plotting indifference points against delay generates a discounting curve fitted to a hyperbolic function, V = A / (1 + kD), where k is the discounting rate and higher k indicates greater impulsivity. Area under the curve (AUC) provides a model-free impulsivity index normalized between zero and one. Additional metrics include choice latency, percentage of large-reward choices per delay block, and omission rate as a measure of task engagement.

ConductMaze automates delay discounting by programming adjusting-amount or adjusting-delay schedules with real-time lever monitoring and pellet delivery confirmation. The system tracks every lever press timestamp, calculates indifference points within each block, and fits hyperbolic and exponential discounting models to session data. AUC, k-values, and choice proportion curves are exported alongside raw event logs. Automated delay escalation and session-to-session titration eliminate manual parameter adjustments across training days.