Purkinje cell (PC) discharge, the only output of cerebellar cortex, involves two types of action potentials, high-frequency simple spikes (SSs) and low-frequency complex spikes (CSs). While there is consensus that SSs convey information needed to optimize movement kinematics, the function of CSs, determined by the PC´s climbing fibre input, remains controversial. While initially thought to be specialized in reporting information on motor error for the subsequent amendment of behavior, CSs seem to contribute to other aspects of motor behavior as well. When faced with the bewildering diversity of findings and views unraveled by highly specific tasks one may wonder if there is just one true function with all the other attributions wrong? Or is the diversity of findings a reflection of distinct pools of PCs, each processing specific streams of information conveyed by climbing fibres? With these questions in mind, we recorded CSs from the monkey oculomotor vermis deploying a repetitive saccade task that entailed sizable motor errors as well as small amplitude saccades, correcting them. We demonstrate that in addition to carrying error-related information, CSs carry information on the metrics of both primary and small corrective saccades in a time-specific manner, with changes in CS firing probability coupled with changes in CS duration. Furthermore, we also found CS activity that seemed to predict the upcoming events. Hence PCs receive a multiplexed climbing fibre input that merges complementary streams of information on the behavior, separable by the recipient PC because they are staggered in time.

Fig 1. The influence of repetitive saccade paradigm on saccade behavior and encoding of primary saccade direction by CSs

Fig 2. CSs encode primary saccade amplitude and duration but not peak velocity during the ‘early post-saccadic period’

(Note: The values of bootstrapped mean ± confidence intervals in Fig 2B, the right panel, are subject to change with every iteration and may not perfectly match the values of the original figure in the manuscript.)

Fig 3. CSs encode corrective saccade direction, amplitude and duration during the ‘post-corrective saccadic period’

(Note: The values of bootstrapped mean ± confidence intervals in Fig 3D, the right panel, are subject to change with every iteration and may not perfectly match the values of the original figure in the manuscript.)

Fig 4. CSs encode the retinal error direction and magnitude during the ‘late post-saccadic period’ in a manner different from primary and corrective saccades

Fig 5. CS activity during the ‘early post-saccadic period’ carries information on primary saccades and errors, whereas during the ‘late post-saccadic period’ it is mostly error-driven

Fig 6. Changes in CS duration encode changes in primary and corrective saccades as well as errors

Fig 7. A trial onset related CS discharge seems to predict the upcoming events

Fig 8. Encoding of different task parameters by individual PCs

SUPPORTING INFORMATION

S1 Fig. Influence of the repetitive saccade task on saccade vigor

S2 Fig. Relationship of CS response to saccade end, CS responses to CF and CP saccades and a comparison of CF and CP saccades made in the same direction in an exemplary PC

(Note: The values of bootstrapped mean ± confidence intervals in S2 Fig C are subject to change with every iteration and may not perfectly match the values of the original figure in the manuscript.)

S3 Fig. Analysis of encoding of primary saccade metrics, separately for CSs in PD_ps and PD_ps+180°

(Note: The values of bootstrapped mean ± confidence intervals in S3 Fig F and H are subject to change with every iteration and may not perfectly match the values of the original figure in the manuscript.)

S4 Fig. Analysis of encoding of corrective saccade metrics, separately for CSs in PD_corr and PD_corr+180°

(Note: The values of bootstrapped mean ± confidence intervals in S4 Fig G, H, I and J are subject to change with every iteration and may not perfectly match the values of the original figure in the manuscript.)

S5 Fig. Primary saccades made in the same direction but resulting in opposite errors evoke similar CS responses

S6 Fig. The influence of primary saccade amplitude in PD_ps and PD_ps+180° with comparable error sizes

S7 Fig. A multiple regression analysis testing the influence of primary saccades and errors on CS activity during non-overlapping post-saccadic periods

S8 Fig. Complementary changes in CS duration and firing rate