Classical conditioning of eyelid and mystacial vibrissae responses in conscious mice.

The murine vibrissae sensorimotor system has been scrutinized as a target of motor learning through trace classical conditioning. Conditioned eyelid responses were acquired by using weak electrical whisker-pad stimulation as conditioned stimulus (CS) and strong electrical periorbital stimulation as unconditioned stimulus (US). In addition, conditioned vibrissal protraction was obtained pairing either weak electrical whisker-pad stimulation or a tone as CS, with a strong electric shock delivered in the whisker-pad as US. This finding suggests that evolutionary pressure has selected a sensorimotor system capable of constructing conditioned responses on the basis of temporal relationships of stimuli, independently of any putative functional purpose.