Modeling the Encoding of Saccade Kinematic Metrics in the Purkinje Cell Layer of the Cerebellar Vermis.

Hari Teja Kalidindi,Egidio Falotico,Thomas George Thuruthel,Cecilia Laschi

doi:10.3389/fncom.2018.00108

Hari Teja Kalidindi, Egidio Falotico + Show 2 more

Open Access

https://doi.org/10.3389/fncom.2018.00108

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Abstract

Recent electrophysiological observations related to saccadic eye movements in rhesus monkeys, suggest a prediction of the sensory consequences of movement in the Purkinje cell layer of the cerebellar oculomotor vermis (OMV). A definite encoding of real-time motion of the eye has been observed in simple-spike responses of the combined burst-pause Purkinje cell populations, organized based upon their complex-spike directional tuning. However, the underlying control mechanisms that could lead to such action encoding are still unclear. We propose a saccade control model, with emphasis on the structure of the OMV and its interaction with the extra-cerebellar components. In the simulated bilateral organization of the OMV, each caudal fastigial nucleus is arranged to receive incoming projections from combined burst-pause Purkinje cell populations. The OMV, through the caudal fastigial nuclei, interacts with the brainstem to provide adaptive saccade gain corrections that minimize the visual error in reaching a given target location. The simulation results corroborate the experimental Purkinje cell population activity patterns and their relation with saccade kinematic metrics. The Purkinje layer activity that emerges from the proposed organization, precisely predicted the speed of the eye at different target eccentricities. Simulated granular layer activity suggests no separate dynamics with respect to shaping the bilateral Purkine layer activity. We further examine the validity of the simulated OMV in maintaining the accuracy of saccadic eye movements in the presence of signal dependent variabilities, that can occur in extra-cerebellar pathways.

Highlights

Saccades are rapid eye movements, observed in primates, carried out to bring a selected spatial target into the center of the fovea
As described in previous sections, the simulated Purkinje cells (PCs) layer activity represents the total amount of inhibitory activity projecting onto each caudal fastigial nuclei (cFN), by the combined burst-pause PC populations organized by their common complex-spike/error property
This CS-off PC layer activity is characterized by an early burst, with an onset prior to the initiation of saccadic movement, followed by relatively milder dip in the activity below baseline, that continues until the mossy fiber (MF) activity persists

Summary

Introduction

Saccades are rapid eye movements, observed in primates, carried out to bring a selected spatial target into the center of the fovea. Lesion and inactivation studies (Zee et al, 1976; XuWilson et al, 2009) carried out in the posterior lobes VIc and VII of the cerebellar vermis, known as oculomotor vermis (OMV), indicate a loss of accuracy and adaptation in the saccadic eye movements This OMV regulated adaptation (Robinson et al, 2006), involves both online correction of sensory-motor signals in the saccade control system to deal with inter-trial variability (Takagi et al, 1998), and long-term corrections for the changes in the mechanical properties of oculomotor plant (Ritchie, 1976; Optican and Robinson, 1980; Robinson, 1995). The organization of the PCs and cFN in the cerebellar vermis and their interactions with the extra-cerebellar regions, responsible for such error correction mechanisms have not been fully addressed

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