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Abstract:
Abstract: Previous functional imaging studies have
demonstrated a role for dorsal cortical circuitry in simple
visually guided saccades (VGS). We have now used fMRI to
investigate cortical activation during the performance of three
tasks involving increasing cognitive demand. (1) In a VGS task,
subjects made saccades to flashed targets. (2) In a compatible
task, subjects made leftward and rightward saccades in response to
foveal presentation of the uppercase words 'LEFT' and 'RIGHT'. (3)
In an incompatible task, on 60% of the trials subjects made
rightward saccades in response to the lowercase word 'left' and
leftward saccades in response to the lowercase word 'right'. The
remaining 40% of trials required compatible responses. When
compared to fixation, the VGS and compatible tasks activated three
dorsal cortical eye fields: the supplementary eye field (SEF), the
frontal eye field (FEF), and the parietal eye field (PEF). In
contrast, the high demand incompatible task, when compared to the
compatible task, activated three additional cortical regions
immediately adjacent to the three eye fields. These areas may
contribute to the suppression of prepotent responses and to the
planning and execution of correct responses when novel visuo-motor
associations are required.
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