Stimulus generalization in mice during Pavlovian eyeblink conditioning

Here we investigate stimulus generalization in a cerebellar learning paradigm, called eyeblink conditioning. Mice were conditioned to close their eyes in response to a 10 kHz tone by repeatedly pairing this tone with an air puff to the eye 250 ms after tone onset. After ten consecutive days of training, when mice showed reliable conditioned eyelid responses to the 10 kHz tone, we started to expose them to tones with other frequencies, ranging from 2 to 20 kHz. We found that mice had a strong generalization gradient, whereby the probability and amplitude of conditioned eyelid responses gradually decreases depending on the dissimilarity with the 10 kHz tone. Tones with frequencies closest to 10kHz evoked the most and largest conditioned eyelid responses and each step away from the 10 kHz tone resulted in fewer and smaller conditioned responses. In addition, we found that tones with lower frequencies resulted in conditioned responses that peaked earlier after tone onset compared to those to tones with higher frequencies. Together, our data show prominent generalization patterns in cerebellar learning. Since the known function of cerebellum is rapidly expanding from pure motor control to domains that include cognition, reward-learning, fear-learning, social function, and even addiction, our data implies generalization controlled by cerebellum in all these domains.Significance StatementConditioned stimuli that resemble each other will evoke a rather similar behavioral response. Here, we investigate this phenomenon of stimulus generalization using Pavlovian eyeblink conditioning to probe cerebellar function. Cerebellum is a brain structure whose known function is rapidly expanding from pure motor control to domains that include cognition, reward-learning, fear-learning, social function, and even addiction. Since we found a strong generalization of the auditory stimulus in eyeblink conditioning, our data implies an important role for generalization in motor and non-motor domains.