Cerebellar inactivation impairs cross modal savings of eyeblink conditioning

Abstract

Eyeblink conditioning using a conditioned stimulus (CS) from one sensory modality (e.g., an auditory CS) is greatly enhanced when the subject is previously trained with a CS from a different sensory modality (e.g., a visual CS). The enhanced acquisition to the second modality CS results from cross modal savings. The current study was designed to examine the role of the cerebellum in establishing cross modal savings in eyeblink conditioning with rats. In the first experiment rats were given paired or unpaired presentations with a CS (tone or light) and an unconditioned stimulus. All rats were then given paired training with a different modality CS. Only rats given paired training showed cross modal savings to the second modality CS. Experiment 2 showed that cerebellar inactivation during initial acquisition to the first modality CS completely prevented savings when training was switched to the second modality CS. Experiment 3 showed that cerebellar inactivation during initial cross modal training also prevented savings to the second modality stimulus. These results indicate that the cerebellum plays an essential role in establishing cross modal savings of eyeblink conditioning.

Figure 1

Cross modal eyeblink conditioning. Mean (± SEM) conditioned response (CR) percentage rats given paired (black circles) or unpaired (white circles) training with CS1 (sessions 1–5) and paired training with CS2 (sessions 6–7). The dashed line separates the sessions for acquisition (CS1) and cross modal training (CS2).

Figure 2

Mean (± SEM) CR percentage during cross modal training with CS2 in 10-trial blocks for rats that previously received paired (paired-paired; black circles) or unpaired (unpaired-paired; white circles) training with CS1. CR percentages from rats that received paired training during phase 1 (paired CS1; gray circles) are included to show de novo acquisition. The dashed line separates the two sessions of cross modal training.

Figure 3

Cerebellar inactivation during CS1 acquisition. Mean (± SEM) conditioned response (CR) percentage during CS1 acquisition (session 1–5), CS1 retention (session 6) and CS2 cross modal training (session 7–8) for control (black circles) and muscimol inactivated (white circles) rats. The dashed line separates the sessions for acquisition (CS1, Drug), retention testing (CS1 retention, No Drug), and cross modal training (CS2, No Drug).

Figure 4

Mean (± SEM) CR percentage during cross modal training with CS2 in 10-trial blocks for rats that received muscimol (black circles) or control (white circles) training during phase 1. The dashed line separates the two sessions of cross modal training.

Figure 5

Cerebellar histology. A. A photograph depicting the location of a cannula tip placement for one rat in the cerebellar interpositus nucleus (IPN). The arrow indicates the location of the cannula tip. B. A photograph that shows a representative example of the spread of fluorescent muscimol (gray areas) to the cerebellar IPN, overlying cortex (HVI), and lateral anterior lobe (ANT).

Figure 6

Cerebellar inactivation during phase 2 acquisition. Mean (± SEM) conditioned response CR during acquisition (session 1–5) and cross modal training (session 6–9) for control (black circles) and inactivated (white circles) rats. The dashed line separates the sessions for acquisition (CS1 Drug) and cross modal training sessions (CS2 Drug and CS2 No Drug).

Figure 7

Mean (± SEM) CR percentage during phase 2 training (sessions 8–9) in 10-trial blocks for rats that received muscimol (black circles) or control (white circles) training during cross modal training (session 6–7). The dashed line separates the two sessions of cross modal training.