The Role of the Fovea and Parafoveal Regions in the Control of “Fast” Optokinetic Responses in the Monkey
It has been well established over the last few years that optokinetic nystagmus in response to high velocity stimuli consists of two components (Cohen et al., 1977): A “fast” component, which has been attributed to the pursuit system and depends on direct visual pathways, and a “velocity storage” component utilizing neural integration through indirect pathways (Robinson, 1980). In response to high velocity stimulation these components manifest themselves in the following manner (fig. 1): the sudden presentation of a high velocity stimulus leads to a rapid increase in nystagmus velocity due to the “fast” component. Next the “velocity storage” mechanism leads to a further, more gradual increase. Thus during high velocity optokinetic nystagmus (OKN) both components are activated. When the lights are turned off, eye velocity shows an immediate initial drop due to inactivation of the “fast” response. The “velocity storage” mechanism decreases more slowly during optokinetic after-nystagmus (OKAN).
KeywordsPurkinje Cell Smooth Pursuit Stimulus Velocity Optokinetic Nystagmus Velocity Storage
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