Essay title __ What is the evidence for neural processes involved in saccadic control? _________________________________________________
Submission date _19 December 2011
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WORD COUNT (excluding title and references) _3437____________________
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What is the evidence for neural processes involved in saccadic control?
The brain can't monitor the entire world at once, so we move our eyes to bring targets onto the fovea for further analysis.) Such high resolution provided by the magnification of the fovea can open up the whole visual field for monitoring (Anstis (1974) & Bouma (1970)). Saccades are a visually controlled motor response of the eye (Findlay & Gilchrist 2003). The eye movement control system enables us to fixate and hold our gaze through moving our eyes 3-4 times a second. The eye muscles themselves are regulated by motor neurons, however both subcortical and cortical brain areas play critical roles in the production and control of saccades. Schiller (1998) proposed two neural pathways for the generation of voluntary and reflexive eye movements: the first being the anterior pathway that flows through the Frontal Eye Fields (FEF) and Supplementary Eye (SEF) Fields to the Brain Stem Generator (BSG); the second being the posterior pathway which flows through the Lateral Interparietal area (LIP) to the Superior Colliculus (SC) and BSG. The action system of saccades controls the incoming visual information in a continuous loop integrating cognition and vision (Findlay & Gildchrist (2003). This essay examines the evidence for neural processes involved in saccadic control of where, when and why we look. IT IS ALL ABOUT WHETHER WE SEE (NOT JUST RESPOND) WITH OUT MINDS OR OUR EYES…OUR HIGHER COGNITION OR OUR SENSORY RESPONSES.
THE IMPORATNCE OF THE SC IN SACCADIC CONTROL
Evidence to support the SC and BSG as the principle subcortical structures involved in saccade generation was identified by Wurtz et al (1982) and Schiller et al (2001). Wurtz et al (1982) found that the SC was a center for the production of overt orienting movements when he found high levels of activity related to overt orienting movement. When stimulated, the SC elicited a saccade (Wurtz et al (1982)). Furthermore the prominent role of the SC in controlled eye movements was demonstrated further when it was removed from a monkey brain (Schiller et al (2001)). Without a SC, electrical stimulation no longer elicited eye movements from the occipital and parietal cortices but continued to do so in the frontal lobe. Further examination by Wurtz et al (2001) identified the superficial layers of the SC to be driven by visual information from the parietal and occipital areas whilst deeper layers related to motor instructions towards the BSG. A motor map of activity is produced in the intermediate layers of the SC where sensory and motor information is integrated. These findings suggest that the SC plays the role of a funnel for primary visual information from a large area of the brain (Schiller et al (2001)).
AT NEURONAL LEVEL- THE SC IMPORTANCE
The collicular neurons: fixation, buildup and burst neurons receive signals from SC, frontal and parietal eye fields. Evidence demonstrates that fixation neurons become less active as the buildup neurons increase in activity preparing for a saccade until
