Purkinje cell number related to rate of classical conditioning

The cerebellar cortex is normally involved (but not essential) in acquisition of the classically conditioned nictitating membrane response. Cerebellar Purkinje cells probably play a role in acquisition, but these cells are vulnerable to hypoxia, ischemia, and aging. Since large age differences exist in rate of conditioning, we suspected that the number of Purkinje cells in individual rabbits would correlate with learning rate. Purkinje cell counts were undertaken in 12 rabbits aged 3-50 months. The correlation between trials to learning criterion and Purkinje cells was -0.79. A second study used 18 3-month-old rabbits. Even with age held constant, the correlation was -0.60. Individual variation in Purkinje cell number accounts for significant variability in learning rate.