Date of Award
2007
Degree Type
Thesis
Degree Name
Doctor of Philosophy
Program
Neuroscience
Supervisor
Dr. Stefan Everling
Abstract
The antisaccade task is an important model of flexible behavioural control. This task requires subjects to inhibit the automatic saccade toward a flashed peripheral visual stimulus and to generate a voluntary antisaccade toward the stimulus’ mirror location in the opposite visual hemifield. Previous functional magnetic resonance imaging (fMRI) studies support the involvement of frontoparietal regions in antisaccade performance. Experiment 1 was designed to dissociate saccade inhibition from saccade generation processes by comparing prosaccades, antisaccades, and nogo trials in a rapid fMRI design. Trials included a task instruction followed by peripheral stimulus presentation and response. Prosaccade, antisaccade, and nogo trial responses were, respectively, to look at the stimulus, look away from it, and inhibit the automatic saccade while maintaining central fixation. Frontal eye field (FEF), supplementary eye field (SEF), anterior cingulate cortex (ACC), intraparietal sulcus (IPS), and precuneus exhibited surprisingly similar activations for prosaccade and nogo responses, suggesting that their fMRI signals might reflect visual detection and attention processes rather than saccade generation or inhibition. Inconsistently with previous studies, Experiment 1 revealed few instruction-related differences. In Experiment 2, we compared prosaccades and antisaccades using half trials to separate instruction- and response-related signals, rather than jittered instruction intervals as in Experiment 1. FEF, SEF, IPS, precuneus, ACC, and left dorsolateral prefrontal cortex (DLPFC) exhibited greater instruction-related activation for antisaccades, demonstrating that a rapid fMRI design can detect instruction-related differences. The first four regions also exhibited greater antisaccade response activation, unlike DLPFC and ACC, which might therefore be involved more in antisaccade preparation and task set rather than execution. In Experiment 3, we looked iii for the saccade inhibition signature not seen in Experiment 1 by comparing frequent prosaccades and rare nogo trials (2:1 ratio). Nogo instruction-related activation was greater in right FEF, DLPFC, IPS, and precuneus, probably due to preparatory and task switching processes. Nogo response-related activation was greater in SEF, ACC, inferior frontal gyrus, and right supramarginal gyrus, probably due to saccade inhibition in nogo trials. Together, these experiments suggest that DLPFC is involved in task set while more posterior regions support a mixture of visual detection, attention, and saccade inhibition processes
Recommended Citation
Brown, Matthew Robert Graham, "fMRI Investigations of Flexible Behavioural Control Based on Eye Movement Models" (2007). Digitized Theses. 5115.
https://ir.lib.uwo.ca/digitizedtheses/5115