Sign-Tracking vs Goal-Tracking
Overview
The sign-tracking versus goal-tracking paradigm classifies individual differences in Pavlovian conditioned approach behavior by measuring whether subjects direct responses toward a reward-predictive cue (sign-tracking) or toward the reward delivery location (goal-tracking). A retractable lever serves as the conditioned stimulus (CS), inserted for eight seconds before delivery of a food pellet into an adjacent magazine. Over successive sessions, sign-trackers develop robust approach, contact, and pressing behavior directed at the lever-CS, while goal-trackers approach the magazine during CS presentation. This individual variation maps onto mesolimbic dopamine circuit differences, with sign-tracking dependent on dopamine release in the nucleus accumbens core.
The Pavlovian conditioned approach (PCA) score integrates three components: response bias (lever presses minus magazine entries, divided by the sum), probability difference (probability of contacting lever versus magazine per trial), and latency score (normalized difference in latency to contact lever versus magazine). PCA scores range from negative one (pure goal-tracking) to positive one (pure sign-tracking), with intermediate subjects classified between negative 0.5 and positive 0.5. Additional metrics include lever contact duration, magazine head-entry rate during CS and pre-CS periods, and the CS-directed approach probability across session blocks to capture acquisition dynamics.
ConductMaze automates the PCA paradigm by controlling lever insertion/retraction timing, pellet delivery, and magazine head-entry detection via infrared beam breaks. The system records every lever press, lever contact, and magazine entry with millisecond timestamps, computing PCA scores and component indices in real time. Acquisition curves showing the emergence of sign-tracking versus goal-tracking phenotypes are plotted across sessions. The platform supports experimenter-defined classification thresholds and exports individual and group-level PCA distributions alongside raw event logs.
Trial Flow
Session Start
Illuminate house light; begin variable pre-trial interval before first CS presentation.
CS Presentation
Insert lever-CS into the chamber for the programmed CS duration.
Approach Recording
Record lever contacts, lever presses, and magazine entries throughout CS period.
CS Offset and US Delivery
Retract lever-CS and immediately deliver food pellet into magazine.
Consumption Period
Allow subject to retrieve and consume pellet; record post-US magazine entries.
PCA Classification
After final session, compute PCA score from response bias, probability, and latency components.
Phenotype Export
Export PCA scores, component indices, and session-by-session acquisition curves per subject.
Session End
Extinguish house light after all trials complete; clean magazine trough.
Parameters
| Parameter | Type | Default | Description |
|---|---|---|---|
| CS Duration | seconds | 8 | Duration of lever-CS insertion before US delivery. |
| Trials per Session | integer | 25 | Number of CS-US pairings per session. |
| Number of Sessions | integer | 5 | Total Pavlovian conditioning sessions for phenotype classification. |
| Inter-Trial Interval (Mean) | duration | 90 s | Mean variable interval between CS presentations. |
| ITI Range | duration | 30-150 s | Minimum and maximum bounds of the variable inter-trial interval. |
| Pellet Reward Size | integer | 1 | Number of pellets delivered as the unconditioned stimulus. |
| PCA Sign-Tracker Threshold | float | 0.5 | Minimum PCA score for sign-tracker classification. |
| PCA Goal-Tracker Threshold | float | -0.5 | Maximum PCA score for goal-tracker classification. |
Metrics
| Metric | Unit | Description |
|---|---|---|
| PCA Score | index | Composite Pavlovian conditioned approach score ranging from -1 (goal-tracker) to +1 (sign-tracker). |
| Response Bias | index | Ratio of lever presses minus magazine entries to total responses during CS. |
| Lever CS Contacts | count | Total number of contacts with the lever-CS per session. |
| Magazine Entries During CS | count | Number of magazine head entries during CS presentation. |
| CS Contact Probability | proportion | Proportion of trials with at least one lever contact during CS. |
| Latency to Lever Contact | s | Mean time from CS onset to first lever contact across trials. |
| Latency to Magazine Entry | s | Mean time from CS onset to first magazine head entry across trials. |
Sample Data
| Subject | Phenotype | PCA Score | Lever Contacts | Magazine Entries (CS) | CS Contact Prob | Lever Latency (s) | Magazine Latency (s) |
|---|
Representative data for illustration purposes. Actual values will vary by species, strain, and experimental conditions.
Applications
- 1Addiction Susceptibility Screening — Identify sign-tracking phenotypes that show heightened cue-triggered drug seeking and relapse vulnerability.
- 2Incentive Salience Research — Dissect dopaminergic mechanisms underlying the attribution of motivational value to reward-predictive cues versus reward locations.
- 3Individual Differences in Pavlovian Learning — Characterize heritable variation in conditioned approach that predicts performance on subsequent instrumental and Pavlovian-instrumental transfer tasks.
- 4Psychostimulant Sensitization — Evaluate how prior amphetamine or cocaine exposure shifts PCA distributions toward sign-tracking phenotypes.
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