Purkinje cell activity during classical eyeblink conditioning in decerebrate guinea pigs.

Purkinje cells are the sole output from the cerebellar cortex and play a critical role during classical eyeblink conditioning. The present study revealed for the first time a learning-related change in individual Purkinje cell activity during successive eyeblink conditioning in decerebrate guinea pigs which permitted continuous single unit recording from the simplex lobe of the cerebellar cortex. The pair-conditioned group received paired presentation of the conditioned stimulus (CS) and unconditioned stimulus (US) until the frequency of the conditioned response (CR) exceeded 80%. The control group received a comparable number of the CS and US in a pseudorandom fashion. Responses of Purkinje cells to the CS were classified into four types: excitatory, inhibitory, a combination of the two, or no response. Approximately half of the recorded cells from both groups changed their response type at various conditioning stages. The firing frequency of a Purkinje cell to the CS showed a tendency to decrease in the pair-conditioned group, while it had a tendency to increase in the pseudoconditioned group. This learning-related difference in change of response type was attributable to a difference in the change between the no response and the inhibitory response types. Correlation analysis of the temporal pattern between the neural activity and the CR revealed that most of the cells that developed an inhibitory response by paired conditioning acquired the CR-related temporal pattern. These results suggest that the learning-related Purkinje cells gain an inhibitory response with a temporal pattern correlated with the CR topography.