Thermal Gradient Preference

The thermal gradient preference apparatus provides a continuous, non-forced assessment of thermosensory function and thermoregulatory behavior in rodents. The system consists of an elongated aluminum runway (typically 100-120 cm long, 10 cm wide) with independently controlled Peltier thermoelectric elements creating a stable, linear temperature gradient from one extreme (5 degrees C, cold) to the other (50 degrees C, hot). ConductMaze drives each Peltier element through a closed-loop PID controller with embedded thermistor feedback, maintaining floor temperature within 0.3 degrees C of setpoint across the entire gradient length. An overhead infrared camera tracks the animal position at 30 Hz while floor-embedded temperature sensors provide real-time correlation between position and substrate temperature. This free-choice paradigm avoids the stress and confounds of forced thermal tests (hot plate, tail flick) by allowing the animal to self-select its preferred thermal environment over extended sessions.

During a standard 30-60 minute session, the animal explores the full gradient and ultimately settles in a temperature zone corresponding to its thermoneutral preference (typically 29-32 degrees C for mice). Thermal allodynia — a hallmark of neuropathic pain — manifests as a rightward shift in preferred temperature (toward warmer zones) following peripheral nerve injury such as chronic constriction injury (CCI) or spared nerve injury (SNI), as the animal avoids normally innocuous cool temperatures that have become painful. Conversely, inflammatory models may show cold-seeking behavior. ConductMaze divides the runway into discrete temperature bins (typically 2-3 degrees C wide) and computes occupancy time, approach/avoidance behavior, and transition frequency for each zone, enabling detailed thermosensory phenotyping beyond a single threshold measurement.

ConductMaze exports position-temperature timecourses, occupancy heatmaps overlaid on the gradient schematic, and zone transition matrices. The software computes preferred temperature (weighted centroid of occupancy distribution), thermal avoidance zones (occupancy below chance level), zone transition count (a measure of exploratory vs settled behavior), and thermal sensitivity index (steepness of the occupancy distribution around the preferred zone). Automated multi-session tracking enables longitudinal studies of neuropathic pain development and resolution, with all gradient calibration logs stored for quality assurance.