Fear Extinction
Overview
Fear extinction is the progressive reduction of a conditioned fear response that occurs when the conditioned stimulus (CS) is repeatedly presented without the unconditioned stimulus (US). Extinction does not erase the original fear memory; rather, it forms a new inhibitory memory that competes with the original excitatory association. This is evidenced by phenomena such as spontaneous recovery (fear returns after the passage of time), renewal (fear returns when tested in the original conditioning context), and reinstatement (fear returns after unsignaled US exposure).
The neural circuitry of fear extinction involves the infralimbic cortex (IL) of the medial prefrontal cortex, which drives extinction learning and recall by activating inhibitory intercalated cells in the amygdala that suppress CeA fear output (Milad & Quirk, 2002). Extinction is a critical translational model for exposure therapy in anxiety disorders and PTSD, where understanding why extinction sometimes fails has direct clinical implications.
ConductMaze automates multi-session extinction protocols with configurable CS-alone presentations, inter-trial intervals, and multi-day scheduling. The software tracks freezing across extinction sessions to generate within-session extinction curves and between-session retention indices. It supports spontaneous recovery, renewal, and reinstatement test sessions with automated context switching.
Trial Flow
Fear Acquisition
CS-US pairings in Context A (Day 1)
Extinction Session
CS-alone presentations in Context B (Day 2)
CS Presentation
CS presented without shock, freezing measured
Inter-Trial Interval
Variable ITI between CS presentations
Within-Session Decline
Monitor freezing decrease across CS trials
Extinction Recall
Test CS-alone next day — retention of extinction
Session End
Record extinction curve and retention index
Parameters
| Parameter | Type | Default | Description |
|---|---|---|---|
| CS-Alone Trials | integer | 30 | Number of unreinforced CS presentations per extinction session |
| CS Duration | seconds | 30 | Duration of each CS presentation |
| ITI Range | seconds | 60-120 | Randomized inter-trial interval range |
| Extinction Sessions | integer | 2 | Number of extinction training sessions |
| Extinction Context | enum | Context B | Context for extinction training (same or different from acquisition) |
| Recall Test Delay | hours | 24 | Time between last extinction session and recall test |
| Criterion | % | 20 | Freezing percentage below which extinction is considered successful |
Metrics
| Metric | Unit | Description |
|---|---|---|
| Early Extinction Freezing | % | Freezing during first 5 CS trials — initial fear expression |
| Late Extinction Freezing | % | Freezing during last 5 CS trials — within-session extinction |
| Extinction Index | ratio | (Early − Late) / Early — within-session extinction magnitude |
| Recall Freezing | % | Freezing during recall test CS presentations — extinction retention |
| Spontaneous Recovery | % | Increase in freezing from late extinction to recall test |
| Trials to Criterion | count | Number of CS trials to reach extinction criterion |
| Renewal Index | % | Freezing when tested in original Context A (context-dependent return of fear) |
Sample Data
| Subject | Group | Early_Ext_pct | Late_Ext_pct | Ext_Index | Recall_pct | Trials_to_Crit |
|---|
Representative data for illustration purposes. Actual values will vary by species, strain, and experimental conditions.
Applications
- 1Exposure therapy modeling — extinction as the laboratory analog of clinical exposure-based treatments
- 2PTSD research — extinction failure, spontaneous recovery, and fear relapse mechanisms
- 3mPFC circuit research — infralimbic cortex role in extinction consolidation and recall
- 4Pharmacological enhancement — D-cycloserine, BDNF, and HDAC inhibitors as extinction facilitators
- 5Memory reconsolidation — boundary conditions between extinction and reconsolidation updating
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