Developmental changes in eye-blink conditioning and neuronal activity in the cerebellar interpositus nucleus

Abstract

Neuronal activity was recorded in the cerebellar interpositus nucleus in infant rats during classical conditioning of the eye-blink response. The percentage and amplitude of eye-blink conditioned responses increased as a function of postnatal age. Learning-specific neuronal activity in the cerebellum emerged ontogenetically in parallel with the eye-blink conditioned response. There were also age-specific changes in neuronal activity after the onset of the conditioned and unconditioned stimuli. The results indicate that the development of the eye-blink conditioned response may depend on the development of stimulus-evoked neuronal responses and learning-specific plasticity in the cerebellum. Functional immaturity in the afferent neural pathways may limit the induction of neural plasticity in the cerebellum and thereby limit the development of the eye-blink conditioned response.

Fig. 1.

Mean ± SEM percentage of conditioned responses (left) from rat pups trained on postnatal days 17–18 (black circles) and postnatal days 24–25 (white circles) across six training sessions (PT, pretraining; * indicates significant group differences). The right displays representative eyelid EMG conditioned responses from rats trained on postnatal days 18 (top trace) and 25 (bottom trace). Calibration: 100 msec. Arrowheads indicate the onset of the CS and the US. PND, Postnatal day.

Fig. 2.

Drawing of a horizontal section of the rat brain with labels indicating the placement of the tips of the electrode bundles for rats trained on P17–P18 (black dots) or P24–P25 (gray dots). Ant IN, Anterior interpositus nucleus.

Fig. 3.

Mean firing rate (spikes per second) of representative units recorded in the cerebellar interpositus nucleus from rats trained on postnatal days 18 (left, PND17–18) and 25 (right, PND24–25) during all 100 trials (top) and nine CS alone test trials (bottom) of training session 5. Arrowsindicate the onset of the CS and US. The gap in unit activity during the US in the top panels is attributable to the stimulus artifact, which precluded recording unit activity.

Fig. 4.

Percentage of single units with significant increases in activity on P17–P18 (black circles) and P24–P25 (white circles) during the first, second, and third CS periods (top) and first, second, and third US periods (bottom) in the pretraining session (PT) and paired sessions 1, 3, and 5 (* indicates significant group differences). PND, Postnatal day.

Fig. 5.

Percentage of neurons with significantly greater activity during trials with CRs relative to trials with no CRs on P17–P18 (black bar) and P24–P25 (white bar). PND, Postnatal day.

Fig. 6.

Mean neuronal activity (normalized to the pre-CS baseline activity) during the CS period for all the single units recorded from the cerebellar interpositus nucleus on P17–P18 (gray lines, PND17–18) and P24–P25 (black lines, PND24–25) in the pretraining session and paired sessions 1, 3, and 5 (* indicates significant bin differences between groups; + indicates group differences).

Fig. 7.

Mean neuronal activity (normalized to the pre-CS baseline activity) during the US period for all the single units recorded from the cerebellar interpositus nucleus on P17–P18 (gray lines, PND17–18) and P24–P25 (black lines, PND24–25) in the pretraining session and paired sessions 1, 3, and 5 (* indicates significant bin differences between groups; + indicates group differences).