Progressive Ratio
Overview
The progressive ratio (PR) schedule is the gold standard for measuring the reinforcing efficacy of drugs, food, and other rewards. In a PR schedule, the number of responses required to earn each successive reinforcer increases according to a defined mathematical function — typically an exponential series such as 1, 2, 4, 6, 9, 12, 15, 20, 25, 32… (Richardson & Roberts, 1996).
The primary dependent variable is the breakpoint — the highest ratio completed before the animal ceases responding for a criterion period. Breakpoint is a direct measure of motivation: animals will work harder (tolerate higher response requirements) for more potent reinforcers. This makes the PR schedule indispensable in addiction research, where it quantifies the motivational valence of abused substances.
ConductMaze automates the entire PR session: it advances the ratio after each reinforcer delivery, monitors the inter-response interval against the session timeout criterion, and logs every lever press with millisecond timestamps. The software supports custom ratio progressions, multiple session termination rules, and real-time breakpoint calculation.
Trial Flow
Session Start
House light ON, levers extended
Active Lever
Subject presses active lever
Ratio Check
Response count ≥ current ratio?
Reinforcer Delivery
Pellet dispensed, cue light 3s
Ratio Increment
Advance to next ratio in series
Timeout Check
No response for criterion period?
Session End
Record breakpoint, retract levers
Parameters
| Parameter | Type | Default | Description |
|---|---|---|---|
| Ratio Progression | enum | Richardson-Roberts | Mathematical function governing ratio escalation (Richardson-Roberts exponential, linear, Hodos arithmetic) |
| Starting Ratio | integer | 1 | Number of responses required for the first reinforcer |
| Step Size | float | 0.18 | Exponential step parameter (for Richardson-Roberts: ratio = 5 × e^(0.18 × step) − 5) |
| Timeout Criterion | seconds | 1800 | Maximum inter-response interval before session termination |
| Max Session Time | seconds | 7200 | Absolute session time limit |
| Active Lever Side | enum | Right | Which lever is reinforced (Left, Right, or Counterbalanced) |
| Cue Light Duration | seconds | 3 | Duration of conditioned stimulus paired with reinforcer delivery |
| Reinforcer Type | enum | Sucrose Pellet | Type of reinforcement (sucrose pellet, food pellet, liquid, infusion) |
Metrics
| Metric | Unit | Description |
|---|---|---|
| Breakpoint | ratio | Highest completed ratio — primary measure of reinforcer efficacy |
| Total Active Presses | count | Cumulative presses on the active lever |
| Total Inactive Presses | count | Presses on the inactive lever (discriminability control) |
| Reinforcers Earned | count | Number of reinforcers delivered before session end |
| Session Duration | seconds | Total elapsed time from session start to termination |
| Post-Reinforcement Pause | seconds | Mean time between reinforcer delivery and next active press |
| Response Rate per Ratio | presses/min | Rate of responding at each successive ratio level |
| Latency to First Press | seconds | Time from session start to first active lever press |
Sample Data
| Trial | Ratio | Active_Presses | Inactive_Presses | Latency_s | PRP_s | Completed |
|---|
Representative data for illustration purposes. Actual values will vary by species, strain, and experimental conditions.
Applications
- 1Addiction research — breakpoint as a quantitative measure of drug reinforcement and craving
- 2Motivation neuroscience — dopaminergic circuit dissection using PR with optogenetic manipulation
- 3Obesity & feeding — comparing reinforcing efficacy of high-fat vs standard diet
- 4Psychiatric drug development — screening compounds for effects on reward motivation
- 5Anhedonia models — reduced breakpoints as translational measure of depression-like behavior
Related Protocols
Compatible Products
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