Semi-automated testing of vibrotactile sensitivity in the rat forelimb

Vibrotactile sensitivity of the hand is correlated with dexterity, yet forelimb sensitivity tests are rarely used in pre-clinical studies due to the lack of standardized equipment and protocols. We developed a vibrotactile detection task to measure forepaw sensitivity in rats. This system consists of a lever with a vibration motor, a force sensor to detect lever grasp, and a pellet dispenser for rewards. Specialized software controls the hardware, delivers stimuli, records responses, and activates rewards. Freely moving rats were trained to hold the lever and release it upon detecting vibration within a time window for a food reward. The correct hit rate generated an S-shaped sensitivity curve, quantifying vibrotactile sensitivity. Rats required approximately five weeks of training to reach baseline performance, with stable detection thresholds over 5 weeks. Desensitization via bupivacaine injection or selective dorsal column lesions increased detection thresholds, indicating reduced sensitivity. Both thresholds returned to baseline after recovery from the anesthetic or injury. To ensure specificity, a second dummy lever, sound maskers, vibration dampeners, and testing in the dark were used to isolate vibration through the paw. Unlike pain (Von Frey) or temperature (Hargreaves) tests, this task quantifies vibration sensation, relevant for clinical settings involving somatosensory dysfunction. This vibrotactile detection task enables high-throughput testing of forelimb vibration sensitivity, offering a clinically relevant tool for studying sensory processing and rehabilitation.