Further evidence that a shared efferent collicular pathway drives separate circuits for smooth eye movements and saccades |
| |
Authors: | M Missal A Coimbra P Lefèvre E Olivier |
| |
Institution: | (1) Laboratory of Neurophysiology, School of Medicine, Université Catholique de Louvain (UCL), 5449 Ave Hippocrate, 1200 Brussels, Brussels, Belgium,;(2) CESAME, Université Catholique de Louvain, Louvain-la-Neuve, Belgium, |
| |
Abstract: | The aim of the present study was to find out whether smooth eye movements (SEMs) evoked by superior colliculus (SC) stimulation
are, as suggested by Breznen et al. (1996), artefactual eye movements resulting from a non-physiological response of the saccadic
generator. This question was reinvestigated in head-restrained cats. Long-lasting SC stimulation was found to evoke, in a
comparable proportion, either a single saccade followed by an uninterrupted SEM or a staircase of two or three saccades interleaved
with SEMs. These two different patterns of eye movements could be elicited at a near-threshold current and at low stimulation
frequencies. In most cases, SEM direction clearly differed from that of the preceding saccade. This difference between SEM
and saccade directions varied in a systematic way as a function of the initial saccade direction. As demonstrated by computer
simulation, this observation can be explained if the neural circuit controlling SEMs reaches a saturation level earlier than
the saccadic burst-generator. Our results in cats were reminiscent of those reported by Breznen et al. (1996) in the monkey
only in some instances, when high frequency stimulation (400–600 Hz) was applied. Indeed, in the case of near-threshold stimulation-elicited
staircase saccades, increasing the stimulation frequency led to a progressive disappearance of the smaller subsequent saccades
that were substituted by uninterrupted SEM-like movements. Altogether, the present results confirm the view that SEMs are
genuine eye movements. These results rule out the hypothesis that SEMs result from a saturation of the saccadic generator
and strengthen the hypothesis that SEMs and saccades are distinct movements. We suggest that the same collicular efferent
cells carry out the motor command to saccadic and SEM circuits and that the position error originating from the SC may be
distributed amongst separate downstream motor systems.
Electronic Publication |
| |
Keywords: | Superior colliculus Smooth eye movements Electrical stimulation |
本文献已被 PubMed SpringerLink 等数据库收录! |
|